A prospective study of neonatal morbidity and mortality was made over four months in 1990 at the neonatal unit in Muhimbili Medical Centre. The incidence of low birthweight (LBW) was 16%. Seven hundred and eighty four LBW infants and 612 heavier infants admitted for care in the unit were followed up for six weeks. The mean birth weight was 2854 grams. LBW carried a seven-fold increased risk of mortality (291/784;37%); this was 64% (291/341) of the total. The risk of morbidity in LBW infants was increased three-fold (436/784;56%) being 73% (436/598) of the total. Factors significantly associated with increased morbidity and mortality were prematurity, birth asphyxia, sepsis, respiratory distress syndrome, hypothermia and hypoglycaemia. The majority of the deaths (83%) occurred within the first week of life.