This report describes an epidemiological investigation of the autistic syndrome using new research diagnostic criteria (Denckla, 1986). The focus here is on the methods of screening and follow-up, and on a description of the cases identified within a circumscribed region of Nova Scotia. Autism, as defined by social deviance, language impairment and repetitive or ritualistic behaviours, has a prevalence of 10 per 10,000 and a male to female ratio of 2.5:1. These findings are discussed relative to those reported previously.