Age variations in the influences of three sets of proximate factors on child survival in Ondo State, Nigeria, during 1981–86 are described. Biodemographic factors covary very strongly with mortality risks during the first month of life, weakly during months 1–11, and imperceptibly beyond infancy. Microenvironmental factors progressively strongly covary with mortality after the neonatal period, while health services accessibility and care factors broadly covary strongly with mortality throughout early childhood. Patterns in the size of the hypothetical population-level impacts of these factors suggest that promoting assisted use of toilet facilities within households by under-5s and wider provision of dispensaries and hospitals would yield cost-effective and notable reductions in overall childhood mortality levels in the study setting.