This randomized, double-blind study is intended to test the safety and feasibility of using 3,4-methylenedioxymethamphetamine (MDMA)-assisted therapy, compared with placebo, to treat social anxiety in autistic adults. Subjects will be randomly (by chance) assigned to receive placebo or MDMA during two experimental sessions. The first six subjects in the study will be randomized to placebo (2) or 75 mg MDMA on the first session and 100 mg MDMA on the second session (4). The next six subjects will be randomized to placebo (2) or 100 mg MDMA on the first session and 125 mg MDMA on the second session (4). The study will explore whether two doses of MDMA, combined with selected therapeutic activities, can reduce social anxiety. The study takes place in Los Angeles, California and requires about 15 visits to the study location over several months. Study subjects will meet with the investigators three times to prepare for the MDMA sessions, and they will meet with them on three occasions and receive daily phone calls for safety monitoring for a week after each session. Blood samples will be collected at baseline, two hours after drug administration during the second experimental session, one month and six months after the second experimental session to measure amounts of the hormones oxytocin, arginine vasopressin and cortisol in plasma. Subjects will return six months after their second experimental session for measurements of and social anxiety and other symptoms and an interview. Subjects will learn what they received at this visit. Subjects who received placebo can go through treatment again to have two sessions with MDMA, the first with 75 mg and the second with 125mg MDMA. Social anxiety, anxiety, depression, stress, self-esteem, empathy, and quality of life will be measured before and after experimental sessions.