This study identified factors associated with support group participation among families of children with autism. A survey was administered to 1005 caregivers of children with autism in Pennsylvania. Two-thirds of respondents (66.4%) had ever participated in an autism-specific support group. In adjusted analyses, demographic characteristics, including age and sex of the child, ethnicity and parental education and income, were associated with support group participation. Parents of children with self-injurious behavior, sleep problems or severe language deficits were more likely to belong, as were parents whose diagnosing clinician referred them to a support group. The results of this study suggest the importance of clinician referrals to groups, and the need to make groups available to under-served populations. (Contains 2 tables.)