Autism Spectrum Disorders are a class of conditions categorized by communication problems, ritualistic behaviors, and deficits in social behaviors. While evidence supporting a genetic component of Autism Spectrum Disorders (ASDs) is strong, no specific genetic marker has been identified. Thus, professionals have had to utilize intelligence tests and measures of adaptive functioning to aid in the diagnosis of individuals with ASD. The present study aimed to isolate specific differences in adaptive functioning in adults with ASD. Two hundred and thirty-four adults with ASD (Autism Spectrum Disorder) or Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS) and intellectual disabilities (IDs) were evaluated with respect to the nature and extent of their independent living skill functioning. The implications of these data for more fully describing and diagnosing autism and PDD-NOS in adults are discussed.