Causes of morbidity and mortality, in children in the developing world, are changing. Cancer is assuming increasing importance. The incidence in such countries is probably substantially underestimated, particularly in relation to brain tumours. However, real differences, from circumstances in industrialized societies, do exist; as in the relative prevalences of leukaemias and lymphomas. Furthermore, some forms of cancer, e.g. Hodgkin's disease and Wilms' tumour, seem to behave more aggressively in children in developing countries. Challenges to be addressed in these areas include inadequate knowledge, resource deficiencies and co-morbidity (especially malnutrition and infection). Solutions lie in approaches to health information and health care delivery systems, health professional education and essential national health research. To these ends, long-term collaboration should be established with colleagues, partner institutions and relevant organizations from more privileged parts of the world.