During a 10 year period, 1971-80, there were 234 children in Great Britain younger than 15 years with a diagnosis of carcinoma registered in Great Britain. These cases represented approximately 2% of all childhood malignant disease. The most common primary site was the thyroid, followed by the nasopharynx and the adrenal cortex. With the exception of adrenocortical tumors, most of the carcinomas occurred in children older than 10 years. In some patients there was a genetic predisposition to neoplasia. Children with carcinomas of the thyroid and female genital tract have an excellent prognosis with 5-year survival rates of over 90%. The prognosis for other sites was generally less favorable; 60% of children with nasopharyngeal tumors were alive at 5 years from diagnosis but less than 20% of those with carcinomas of the gastrointestinal tract or the adrenal cortex.