Information about the causes of infant and early childhood (1-4 years) mortality was compiled from the vital registration system for the Western Area, records from the children's Hospital in Freetown and two demographic sample surveys conducted in various chiefdom headquarters towns around the country. The leading causes of infant mortality are tetanus, fevers, measles and diarrhoea. A breakdown of certified deaths in infancy showed that tetanus is quite important in the neonatal period accounting for as much as 68% of neonatal deaths. Measles and diarrhoea were the leading causes of death in the last 6 months of infancy. The leading causes of early childhood deaths were measles, diarrhoea and fevers. Nutritionally related diseases such as measles and diarrhoea were seen to account for up to 40% of all early childhood deaths. The major factors affecting these causes of death were childbirth and childcare practices in the case of tetanus and the nutritional status of the children in the case of measles and diarrhoea. The majority of deliveries were still being performed by Traditional Birth Attendants in very unhygienic surroundings which it was felt contributed significantly to the high incidence of neonatal tetanus. At the other childhood ages the poor nutritional status of the majority of children in Sierra Leone as shown by the results of the 1978 National Nutrition Survey was seen as the significant factor. The effects of the identified major causes of infant and early childhood mortality (tetanus, fevers, measles, and diarrhoea) can be largely diminished by effective intervention programmes such as oral rehydration therapy and the training of Traditional Birth Attendants.