Examining outcomes such as quality of life among patients with chronic conditions is important to better understand the impact of these illnesses on children and adolescents. This study followed a cohort of more than 600 adolescents with chronic illness at a mean age of 16 years into adulthood, at a mean age of 33 years. Adolescents with chronic physical illness had a measurably lower quality of life as adults than their healthy peers. Adolescents with Axis I psychiatric disorders had more problematic social relationships as adults, and those with personality disorders had later problems with social relationships, psychological well-being, and impaired role functioning. Mental disorders among adolescents appear to have a greater impact on adult quality of life than do chronic physical illnesses.