The objective of this study was to refine the Children's Social Behavior Questionnaire (CSBQ), to reduce its length, and to verify its psychometric properties. The CSBQ is a questionnaire for parents or caregivers of children with PDD. The items describe a broad range of features that are typical of PDD, particularly in its milder forms. Based on conceptual judgment and factor analyses, the number of items was reduced from 96 to 49. Six subscales were constructed to allow a differentiated description of PDD problems. Estimates for internal, test-retest, and inter-rater reliability, and for convergent and divergent validity were good. Different clinical and control groups showed the hypothesized patterns in nature and degree of their problems.