An estimated 8,600 new cases of cancer are expected to be diagnosed in children aged 0-14 in the United States during 2001. Childhood cancer rates vary considerably by age with rates of 20.1 cases/100,000 for ages 0-4, 10.8 cases/100,000 for ages 5-9, 12.0 cases/100,000 for ages 10-14, and 19.6 cases/100,000 for ages 15-19. While the overall cancer mortality rate among children aged 0-14 declined by an average 2.9% per year during the time period 1975-1998, the overall incident rate, as measured by the National Cancer Institute's (NCI) Surveillance, Epidemiology, and End Results (SEER) Program, increased by an average 0.8% per year. Concern over the increasing incidence rate has led to increasing public demands for research on the causes of childhood cancer and for research on patterns of care among children and adolescents with cancer. Several groups have proposed that a national childhood cancer registry would enhance research opportunities. The NCI is proceeding to develop a National Network for Research on Cancer in Children which among other components would include merging databases of the NCI's Childhood Cancer Group (CCG) and the Pediatric Oncology Group (POG) to create a National Childhood Cancer Registry (NCCR). However, several studies have documented that the CCG and POG do not enroll all children with cancer in the US, and that they enroll even fewer adolescents. A recent tabulation of the California Cancer Registry (CCR) database for cases diagnosed in 1996 showed that 74.6% of childhood cancer cases among ages 0-14 were reported to the CCR by CCG/POG facilities but only 37.2% of cases among ages 15-19 were reported by those same facilities. Therefore, it is well recognized that the NCCR will need to collaborate with state and SEER population-based cancer registries in order to obtain complete case ascertainment. Similarly, the Centers for Disease Control and Prevention (CDC) National Program of Cancer Registries (NPCR) has been investigating methods for states to: (1) efficiently collect incident cancer case reports including childhood and adolescent cancers, (2) validate completeness of state case ascertainment, and (3) increase the research potential for NPCR-collected data.