The reliability and construct validity of ratings for the Autism Behavior Checklist were examined with a sample of 198 children diagnosed with autistic disorder and conditions often confused with autism. Alpha coefficients for the five scales of the ABC as well as the Total Score were reported and the factor structure of the ABC was examined through confirmatory factor analysis. The results of the reliability analyses indicated that the Total Score alpha coefficient of the ABC was adequate for screening purposes, but the reliabilities of the scales were not. Confirmatory factor analyses indicated some support for alternate four- and five-factor models. (Contains 2 tables and 2 figures.)