The psychometric properties of the Pervasive Developmental Disorders Rating scale (Eaves, 2003) and the Gilliam Autism Rating Scale (Gilliam, 1995) were investigated in this study. One hundred thirty-four individuals with autism, other pervasive developmental disorders, or conditions frequently confused with autism participated in the study. The results indicated that, with one exception, the reliability of the scores from both instruments met or exceeded standards for use in screening decisions. The reliability of the total scores from both instruments exceeded 0.90. Validity coefficients computed between the two sets of scores indicated that the instruments measured similar constructs (e.g., r [subscript pddrs total x gars total] 0.84). The scores from both instruments discriminated between children with autism and children who were not autistic to a statistically significant degree. (Contains 5 tables.)