The International Classification of Childhood Cancer (ICCC) updates the widely used Birch and Marsden classification scheme. ICCC is based on the second edition of the International Classification of Diseases for Oncology (ICD-O-2). The purpose of the new classification is to accommodate important changes in recognition of different types of neoplasms, while preserving continuity with the original classification. The grouping of neoplasms into 12 main diagnostic groups is maintained. The major changes are: (1) intracranial and intraspinal germ-cell tumours now constitute a separate subgroup within germ-cell tumours; (2) histiocytosis X (Langerhans-cell histiocytosis) is excluded from ICCC; (3) Kaposi's sarcoma is a separate subgroup within soft-tissue sarcomas; (4) skin carcinoma is a separate subgroup within epithelial neoplasms; (5) "other specified" and "unspecified" neoplasms are now usually separate sub-categories within the main diagnostic groups. Draft copies of the ICCC were distributed to some 200 professionals with interest and expertise in the field and their comments are considered in this final version. This classification will be used for presentation of data in the second volume of the IARC Scientific Publication "International Incidence of Childhood Cancer." A computer programme for automated classification of childhood tumours coded according to ICD-O-1 or ICD-O-2 is now available from IARC.