Italian researchers have suggested that there may be two subtypes of autism, inflammatory ASD (I-ASD) and non-inflammatory-ASD (NI-ASD).
Those subjects with inflammatory ASD are likely to exhibit chronic and/or recurrent sino-pulmonary infection, asthma and persistent GI symptoms with high frequency non-IgE mediated food allergy. Those with this subtype are more likely to have a better response to antinflammatory therapies such as helminthic therapy than are those with non-inflammatory ASD
Significant results have been observed over a 4-5 year period in 70% of those with inflammatory ASD who took TSO in its original pH2.7 form, and the improvements observed were not only in the quality of stool and control of allergic symptoms, but also in improved behaviour and cognitive skills.
For more detail about this, see this post and this support group thread.
The science on helminthic therapy and autism
For more research, use your device's search function (the 'Command' and 'F' keys on a desktop or laptop, or 'Find in page' in the drop-down menu from the three dots icon on a mobile) to search the following page for "autism" and "ASD".
Media coverage of helminthic therapy and autism
- Supplements, worms and stool: How families are trying to game the gut to treat autism traits - Leah Shaffer, Spectrum
- Sid Baker: Beetlejuice! Beetlejuice! Beetle Larvae? – #311 - Dave, Bulletproof (autism)
- Microbiome Research in Autism Spectrum Disorders - William Parker (Helminths mentioned from 34 minutes)
- Helminths: ASD Cause or Potential Treatment - William Parker, Autism Research Institute
- Testing the use of helminth worm ova in treating autism - Eric Hollander, Simons Foundation
- An Immune Disorder at the Root of Autism - Moises Velasquez-Manoff, New York Times
- Biome normalization using Hymenolepis diminuta (HDC) - Judith Chinitz, CDePalma (autism)
- Got Bugs! - William Parker, AutismOne
- Autism/TSO Presentation Part 1 - Stewart Johnson on the use of TSO as a treatment for certain symptoms of autism, Mt. Sinai Autism Conference, 2007, YouTube
- Autism/TSO Presentation Part 2
- Autism/TSO Presentation Part 3
Anecdotal reports about under 18s with autism (ASD)
The results have been dramatic. My son’s most extreme behaviors, including self-abuse (head hitting, hand biting), agitation, aggression, anxiety, obsessive/compulsive thoughts and behaviors, impulsivity, perseveration, behavioral inflexibility, extreme sensitivity to external stimuli, and “stimming” were completely eliminated 10 weeks into the therapy, and have not returned for 15 months now. 
My son, who is 15, is on the autism spectrum, is gay, overweight, fatigued, depressed, and has PANDAS/POTS and OCD, along with mast cell and allergy issues. The list is long! He started using helminths to treat the PANDAS. The first dose was 5 NA in November 2019, then a second dose of 5 in May 2020. He has always struggled with being awkward and different, and had difficulty expressing what he was feeling, but I didn’t realise just how severely depressed he had become. When he told me how much he had hated himself for so long, it broke my heart. His anxiety was off the charts. He said he was suicidal. Fortunately, a month on helminths has cleared his brain. He wakes up early now, and has lost 15 lbs. It’s like night and day, like a switch turned off and his inflammation is gone, and I am so thankful for this. I wish I had given NA to him 5 years ago. He's doing so great on them. Helminths have literally saved his life. 
Three comments by a parent/therapist
… he and the other children who received hookworm all improved cognitively and in motor skills. Why those 2 things, I don't know. Most of the younger children, the less impaired, also improved, sometimes dramatically, in expressive language… There are many children with TSO now, and the results with that have been remarkable. It seems to have about a 70-75% success rate of causing major global improvement. One child I know was non-verbal and on TSO began to talk. He's now fairly chatty. A lot is repetitive language, but a lot isn't. His teachers couldn't believe it. (Link expired)
My older son is 16 and autistic. I started with TSO 3 years ago and within 12 weeks or so, began to see positive results in terms of digestive symptoms, mood, and eventually cognition. Because of the staggering cost, I moved him onto first hookworm and then added TTO when it became available. I now have many, many clients using some form of helminths with a positive result rate (I estimate) around 75% (at least). Things that improve: cognition, receptive language, eye contact, sociability, awareness (less autistic fog), sometimes expressive language, and absolutely gut symptoms. Things I haven't seen affected so much in the autism population - anxiety and OCD. (Link expired)
I have been using TSO in my son with autism and many of clients and friends' children have also been on this, so I have a fair bit of experience with it at this point. Almost all children require the full 2500 ova every 2 weeks for maximum efficacy. Most take an average of 10-14 weeks at this full dose to start to show improvement, although that is an average - some take a shorter amount of time, some longer. The first thing to improve tends to be bowel symptoms. Starting around 14 weeks, parents start to see improvements in communicative intent, sociability, receptive language. The younger and less severe the child, the more improvements are seen, although even older and more affected kids like my son have done incredibly well on TSO. (Link expired)
TSO and HDC have both been found generally effective in autism, and NA may help with some of its co-morbidities, but individuals can respond uniquely to the different helminths.
We started with 15 NA in 2016 for my autistic PANDAS daughter but her flare was under control with azithromycin so the side effects were not as bad. The second inoculation was 20 NA and the reaction was pretty severe, her psychiatric symptoms worsened. She was already in a flare up when I inoculated. Side effects lasted about 6 weeks then started having better days until she achieved remission exactly at week 11. We also tried 10 HDC which was amazing quick results but my daughter ended up with horrible cramps so I never tried them again. I control side effects of third inoculation of 20 NA with TSO (500 each week) and it worked out well. Fourth inoculation was 10 NA 3 months after the 20 and the side effects were a lot milder and she achieved remission at 12 weeks post inoculation of that last batch of 10.  
When using helminths in children with autism, they should be introduced VERY gradually to avoid triggering severe side effects.
Started off 500 (TSO), two weeks later 1000, two weeks later 2500. He is having really bad behaviors… hitting screaming.” (From a parent treating his 17 year old son with autism.) 
My child is autistic and as long as we increased the dose VERY SLOWLY he was fine. When we doubled the dose he went absolutely bonkers... I think with the ASC population you have to be very very careful with these things... 
Once smaller doses of TSO have been tolerated, 2,500 ova has been found to be best dose size in most cases.
… even the little ones seem to need the maximum. I've only seen 2 or 3 kids ever who did better with lower dose, and even they were on at least 1000. (Link expired)
I give TSO 2500 to my 16 year old son with autism and it acts like a “happy pill” for him - I think his body feels so much better. He is not particularly verbal, so I can’t ask him about side effects, but I’m sure if there were any negative ones I would definitely be able to tell from his behavior. He takes the salty liquid like a champ, makes a face, and then goes about his business. 
For a further collection of reports, see the following page:
Anecdotal report about an adult with autism
After being on TSO for 4 months, my adult daughter was able to reduce her medications for OCD, and she has not had her usual severe seasonal depression during the recent winter. After taking the first 10 doses of 2500 TSO, she was able to reduce her dose without losing any benefits. (Via private message.)
The role of the microbiota in autism
Worms and bacteria are known to interact in complex and subtle ways to provide an efficient and beneficial ecosystem.
The role of gut bacteria in autism is therefore arguably as important as that of helminths, and the two are likely to be complementary in addressing this disorder.
He then tells a surprising story about a woman whose son had autism. She persuaded a physician to prescribe vancomycin to change the child’s microbiota, and the autism disappeared. But it returned when he went off the drug. The experiment was resumed, and the autism went away again. And a fecal transfer had a lasting effect so that more than a decade later, the young man works in a microbiology lab. 
In view of the articles above, Fecal Microbiota Transplantation (FMT) might be worth considering for autism, either alone or in combination with helminthic therapy. For more about combining these treatments, see the following page.
Asperger (Asperger’s) syndrome
The limited feedback received so far from those with Asperger’s who are hosting helminths suggests that, while this therapy may not change the unique features of Asperger’s, it may make positive changes to health that can improve the life of someone with this form of autism.
I'm definitely still aspie but the fun part of using helminth therapy is that I have tons more energy, mind clarity (which allows me to understand people way better and estimate better what a proper reaction is in social situations). And because I feel so much better, I'm more cheerful, less rigid, thinking less in black and white. Thankfully my obsessive hobbies, hyper-focusing, the need to recharge on my own, etc., are still parts of me. 
Almost 12 years with NA has transformed my health in many ways, but I'm just as much as Aspie today as I was before HT. And I'm actually very comfortable about this, because my difference has given me abilities that I've been able to put to good use in life, even though it has also caused difficulties, both for me, and for those close to me… Worms may do for you what they've done for me - leave you with the "good" aspects of Asperger's but greatly reduce the fog and fatigue.