In order to differentiate the behavioural profiles in autism and mental retardation and to cross-validate a behavioural autism screen, 84 subjects with autism (64 males and 20 females) with a mean age of 10 years selected from a Swiss national survey were compared to a control group of 84 subjects matched by age and gender with mental retardation, but without autistic features. The behavioural profile was assessed using the Developmental Behaviour Checklist (DBC). The behavioural profile in autism, in contrast to mental retardation, was marked by higher scores in the domains of disruptive, self-absorbed, communication disturbed, anxious and autistic behaviour, and a higher total DBC score. Furthermore, a higher vulnerability for behavioural abnormalities became evident for females with autism. A recently proposed DBC-Autism Screen was cross-validated, and a slight extension of the screen led to even higher correct classification rates. It was concluded that the DBC is a suitable instrument for the assessment of the behavioural profile and for screening in autism.