This study investigated parental beliefs about the etiology, diagnosis, and treatment of autism spectrum disorders. Sixty-two families of affected children completed a questionnaire asking when the parent first noticed developmental or behavioral problems, when they were told the diagnosis, how confident they were about the ability of their child's physician to recognize autism, whether they believed anything specific might have caused their child's autism, and what medications and complementary or alternative therapies they had tried. Two-thirds of parents suspected a specific cause, and three-quarters questioned their physician's ability. Parents who perceived a greater delay in diagnosis or who had tried more different therapies both tended to have less confidence in their physician (p = 0.20 and p = 0.07, respectively). Physicians should inquire about parental beliefs concerning etiology, learn what treatments the children are receiving, perform screening at the 18 month visit, and make referrals for further evaluation as soon as a child begins to exhibit signs suggestive of autism. (Contains 2 tables and 1 figure.)