We videotaped 24 children, adolescents, and young adults with autism, individually matched for chronological age and verbal mental age with 24 nonautistic persons with mental retardation, for their spontaneous and prompted greetings and farewells towards an unfamiliar adult. Compared with control subjects, those with autism were less likely to offer spontaneous verbal and nonverbal gestures of greeting and farewell, and were less likely to establish eye contact even when they were offered a greeting. There were also fewer autistic subjects who smiled, or who waved goodbye. Results corresponded with raters' subjective judgments of participants' interpersonal engagement with the stranger. One interpretation of the findings is that they reflect a relative lack of intersubjective engagement by autistic individuals.