The aim of this study was to determine for the first time neurosteroid levels, dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEA-S) in particular, in a group of adult patients with autistic disorder and compare these levels with normal healthy individuals. Levels of DHEA, DHEA-S and cortisol were compared between 15 adult drug-free patients with autistic disorder and 13 healthy controls. The Ritvo-Freeman Real-Life Rating Scale (RLRS) and the Overt Aggression Scale (OAS) were assessed as a measure of symptom severity. Significant lower DHEA-S levels were observed in the group with autistic disorder as compared to controls (p < 0.05). DHEA-S levels appear to be low in patients with autistic disorder and, while speculative, may play a role in the etiopathophysiology of the disorder.