Asperger syndrome (AS) is differentiated from high-functioning autism (HFA) largely on a history of “language delay.” This study examined “specific language impairment” as a predictor of outcome. Language skills of 19 children with AS and 45 with HFA were assessed at 4–6 years of age (Time 1) and 2 years later (Time 2). Children’s symptoms and functional outcome scores were assessed every 2 years (Times 3, 4, and 5) until ages 15–17 years old. Regression analysis revealed that specific language impairment at time 2 more often accounted for the greatest variation in outcome scores in adolescence than the standard diagnosis of AS versus HFA based on history of language delay. Diagnostic implications are discussed.