Incidence rates of cancer among children aged 0-14 for the period 1970-79 have been generated with the use of data from the Greater Delaware Valley (GDV) Pediatric Tumor Registry. This population-based registry covers a 31-county area and has a pediatric base population of 2 million. During the period, approximately 2,300 cases of childhood cancer were diagnosed in the region. Incidence rates for all histologic types combined are similar to rates from other large surveys conducted in the United States and Western Europe. However, certain histology-specific rates in the GDV vary by race. In the GDV nonwhites relative to whites have higher rates of Wilms' tumor, soft tissue sarcomas other than rhabdomyosarcoma, and retinoblastoma. These contrasts are supported by surveys in African populations showing relatively higher rates of these tumors among African black children. GDV whites exceed nonwhites in incidence of acute leukemia, neuroblastoma, and Ewing's sarcoma. African black children also experience low rates of these tumors. The frequency of central nervous system tumors is similar for GDV whites and nonwhites, despite reports of a rarity of these neoplasms in African blacks. Variations in incidence rates reveal population subgroups with particular tumor susceptibilities and may provide clues as to the relative influence of heredity and environment on patterns observed.