- Two childhood cancer registries exist in Ontario. One (POGO) accrues by active registration by pediatric cancer centers, utilizing a histologically based classification system. The other accrues by passive linkage within a larger adult oriented cancer registry (OCR) using a topographically based classification. A reportedly high incidence of childhood cancer based on the latter registry prompted a comparison of the content of the two registries over a 2-year period with the hypothesis that there would be systematic accrual errors. All registrations in both registries for the specified period were reviewed systematically and validated by pathology reports. A small number (2.6%) of registrations in the passive registry were not incident cases, while 2 particular pathologic diagnoses were included in the histologically based registry and not the topographically based registry. These were low grade gliomas and Langerhans cell histiocytosis (LCH). The validated annual incident rate (15.6 per 100000 children 0-14 years of age, excluding LCH) is slightly higher than that reported in other industrialized countries. Ninety-six percent of children aged 0-14 were treated in pediatric oncology centers, while only 46% of adolescents aged 15-17 were treated in such centers. Of the remaining adolescents, more than one-third had lymphomas. This maldistribution of care provided for the young adolescent population may compromise their survival prospects. The results of this study should prompt revision of health care policy and patterns of service delivery.