The mortality rates (MRs) of children under 5 years of age in the various population groups of the RSA were calculated as deaths/10(5) for various causes of death and groupings of causes of death as classified by the International Classification of Diseases. In 1970 the ten leading causes of death among Coloured and Black children under 5 years of age in the RSA were similar to those among children in developing countries. The rank order of causes of death (in MRs/10(5] among Coloured children was as follows: gastro-enteritis (1 733), pneumonia (725), immaturity (405), ill-defined causes of death (168), nutritional deficiencies (167), measles (126), anoxia (97), 'other bacterial diseases' (91), inflammatory diseases of the nervous system (55) and tuberculosis (48). The ten leading causes of death among White children in the RSA were characteristic of children in Western developed countries. The rank order (in MRs/10(5] was as follows: immaturity (144), anoxia (94), pneumonia (46), gastro-enteritis (41), congenital heart disease (32), other accidents (19), birth injury (19), ill-defined causes of death (12) and inflammatory diseases of the nervous system (11).