Adolescent perceptions of the impact of illness were measured through the administration of an original questionnaire to 345 healthy adolescents and 168 adolescents with diabetes mellitus, cystic fibrosis, cancer, and cardiac, renal, or rheumatologic diseases. Total impact of illness (e.g., leukemia or colds) did not differ between ill and healthy respondents, and the nature of adolescent concerns were similar for both groups. Restriction of freedom was seen as the major disruption brought about by illness, with other areas of impact including relations with peers, siblings, and parents. Adolescents with cancer were most likely to view treatment as highly disruptive and, along with rheumatologic patients, expressed greatest disruption of body image secondary to disease and treatment. Perceived school disruption was most common in cardiac and oncologic patients, with the former also expressing a high degree of concern about sexuality. Females in all groups reported more impact of illness on physical appearance than did males; this difference was greatest in adolescents with cancer, rheumatologic diseases, and cystic fibrosis. The essentially healthy psychologic status of chronically ill adolescents is noted, as is the generally hopeful and positive quality of patient responses.