In the study of international childhood cancer incidence coordinated by the International Agency for Research on Cancer, carcinomas were generally rare, with an annual incidence for most sites nearly always under 1/1 million. Liver carcinoma was most common in parts of East Asia, Oceania, and Africa, where it is also common among adults and hepatitis B infection is widespread. Adrenocortical carcinoma had an incidence in Sao Paulo, Brazil, of 1.5/1 million, more than three times the rate in most other registries, indicating the presence of either a specific environmental risk factor acting before or around the time of birth or a concentration of genetically susceptible persons. Thyroid carcinoma seldom had a recorded incidence of more than 1/1 million, and variations in recorded rates may reflect differences in frequency of diagnosis rather than variations in risk. In East Asian populations, who have the highest incidence of nasopharyngeal carcinoma among adults, the childhood incidence of this cancer was moderately elevated. By far the highest incidence in children was found in North Africa, a region of intermediate risk for adults. In the United States the incidence among Black children was nine times that among Whites. Genetic and environmental factors may both be involved in the striking ethnic and geographical distribution. Oral carcinoma in childhood had a high relative frequency in Bangladesh. In the United States, the incidence among Black children was three times that among Whites. Skin carcinoma had an exceptionally high frequency in Tunisia, associated with the unusually high prevalence of xeroderma pigmentosum.(ABSTRACT TRUNCATED AT 250 WORDS)