The Pervasive Developmental Disorders Rating Scale (PDDRS; Eaves, 1993) is a screening instrument used in the assessment of autistic disorder. In this study, the reliability of test scores for the PDDRS was examined with three samples. The first sample consisted of 456 participants ranging in age from 1 to 12 years old and the second sample consisted of 111 participants in the 13 to 24 year-old range. Additionally, the test-retest reliability of scores for the PDDRS was examined with a sample of 40 participants. The results indicated that coefficient alpha for the PDDRS Total Score was adequate for screening purposes (r = .89) for both age groups. The results of the test-retest study also suggested that PDDRS had adequate test-retest reliability (r = .92) for the PDDRS Total Score. © 2002 Wiley Periodicals, Inc. Psychol Schs 39: 605–611, 2002.