A retrospective study of birthweights, the incidence, and possible aetiology of low birthweight in 31,490 Nigerian children, delivered in two hospitals at Ibadan, is reported. The important findings were: (a) mean birthweights for males (3,000 gm), and for females (2,880 gm) in a non-teaching hospital were significantly higher than 2,980 gm and 2,860 gm for males and females respectively in the teaching hospital; (b) the mean birthweights for boys were significantly higher than those for girls in both hospitals; (c) these mean birthweights, though generally higher than previous reports from Nigeria, were significantly lower than those for North American Caucasian and Negro babies, and of babies of three different racial groups in Malaysia. Other interesting, though expected findings were: (a) a high incidence of low birthweight (15.5 per cent) and (b) a high incidence of small for dates babies (60 per cent). It is suggested that since birthweights, the incidence of low birthweight and its aetiology are vital in the planning of health care in any country, a prospective study involving many urban and rural areas of the country and including factors known to influence birthweight should be undertaken.