Children with developmental or psychiatric disorders often have problems with social interaction. This study reports on the development of the Ghuman-Folstein Screen for Social Interaction (SSI), a parent/caregiver questionnaire designed to measure the capacity for basic social interaction skills across a variety of contexts in preschool children. The SSI was administered to 51 clinically referred children with a high probability of deficits in social interaction and 60 healthy control subjects to establish reliability and validity. The children were 24 to 61 months of age, with diverse ethnic and socioeconomic backgrounds. Strong internal consistency, significant correlation for test/retest reliability, moderate correlation for interrater reliability and support for external validity of the SSI was established. The SSI scores differentiated between the clinically referred subjects and healthy control subjects and between children with pervasive developmental disorder (PDD) of the autistic type and other non-PDD developmental disorders. The SSI is a relatively simple, efficient, reliable, and valid measure for the capacity for basic social interaction skills in children 24 months to 5 years of age. The SSI has a potential to be useful in primary health care settings to identify children at risk who may need tracking and/or further evaluation and treatment services.