It is now known that autism is a lifelong handicapping condition. While some of the characteristic behaviors of autistic children remain unchanged in adolescence and adulthood, there is evidence that other behaviors change as a function of development. Assessment instruments for identifying autism are generally intended for use with. young children and may not accurately assess autism in adolescents. Two studies compared autistic adolescents with matched autistic children and nonautistic adolescents on two autism rating scales. The validity of the Childhood Autism Rating Scale for use with adolescents was supported while the validity of the Prescreening Checklist was questioned. The findings were discussed in relation to the age-related changes which occur in autistic adolescents.