In this study, the authors examined the construct validity of the Pervasive Developmental Disorder Rating Scale (PDDRS; R. C. Eaves, 1993), which is a screening instrument used to identify individuals with autistic disorder and other pervasive developmental disorders. The PDDRS is purported to measure 3 factors--arousal, affect, and cognition--that collectively make up the construct of autism. Using scores from 199 children (aged 1-6 years) diagnosed with autistic disorder, the authors submitted data to exploratory and confirmatory factor analyses. In the 1st series of analyses, the authors analyzed a user-specified 3-factor solution using principal axis factor analysis with a promax rotation to evaluate the assertion of a correlated 3-factor structure. Next, the authors analyzed 1-factor and 2-factor solutions to determine if they provided a better factor structure for the data. In the 2nd series, the authors conducted confirmatory factor analyses, which compared the theorized hierarchical 2nd-order factor model with 5 plausible competing models. The results of the exploratory analyses supported the 3-factor solution. With the confirmatory analyses, the 2nd-order factor model provided the best fit for the data. The exploratory and confirmatory analyses supported the theoretical assumptions undergirding the development of the PDDRS. The authors discuss theoretical implications, practical implications, and areas for further research. (Contains 7 tables and 6 figures.)