Medication treatments for core symptoms of autism spectrum disorder (ASD) continue to be unmet medical needs. The only medications approved by the U.S. Food and Drug Administration (FDA) for the treatment of individuals with ASD are effective in treating irritability and associated aggressive behaviors, but these medications can also cause severe long-term side effects such as diabetes and involuntary motor movements. Therefore, effective medications with more tolerable side effect profiles are highly desirable. This profile is consistent with pregnenolone (PREG). PREG belongs to a new class of hormones known as neurosteroids, which have been shown to be effective in treating various psychiatric conditions including bipolar depression and schizophrenia. As compared to currently FDA-approved medications, our preliminary data suggested that PREG may represent a potentially effective and well-tolerated agent for treating irritability in individuals with ASD. In addition, our experience suggests that PREG might be helpful in improving selected core symptoms such as social deficits and sensory abnormalities of ASD. This study provides the opportunity to further explore the usefulness of PREG in the treatment of irritability and some core symptoms of ASD. We are performing a 12-week randomized double-blind controlled pilot trial to examine the effectiveness of orally administered PREG in reducing irritability and associated behaviors in adolescents with ASD. In this study, we also aim to examine the usefulness of biomarkers (blood levels of neurosteroids, eyetracking and brain wave recording) in predicting treatment response and assessing biologic changes with PREG treatment.