This study examined the association between adaptive behavior and general cognitive level in individuals with autism or PDD-NOS with and without comorbid mental retardation. Data from the screening version of the Vineland Adaptive Scales and the Wechsler Intelligence Scales were analysed in a sample of 67 subjects. While in the higher functioning individuals (IQ > 70, n = 34) IQ and adaptive behavior level differed significantly, performances were fairly comparable in subjects showing lower cognitive functioning (IQ < 70, n = 33). Regression models revealed a higher correlation between IQ and single adaptive behavior domains in the non-mentally retarded participants, with the domain Communication reaching the highest predictive power of the single adaptive behavior areas. Findings indicate, the relationship between adaptive and cognitive function in autistic disorders is mediated by the presence of a qualitative reduction of intelligence. Methodological limitations of the study are discussed.