Carcinomas occur rarely in children and adolescents. Despite their rarity, these tumors present a unique opportunity to assess theories of origin because the interval from birth to tumor onset is relatively short compared with that seen in adults. We describe the clinical and demographic characteristics of 151 patients younger than 20 years of age with carcinomas who were treated at a pediatric cancer center having a large referral area. Incidence data for the major types of carcinomas in children, based on unpublished data provided by the National Cancer Institute's Surveillance, Epidemiology and End Results Program (SEER), also are reported.