A retrospective and cross-sectional study of low birth weight (LBW) incidence in Ibadan, Nigeria, was conducted covering the period 1995-2005. LBW is defined by the World Health Organization (WHO) as birth weight less than 2500 g. It is a serious threat to survival in both perinatal and neonatal periods, and to normal physical and mental development in the post natal period. The study was aimed at gaining understanding on the determinants of LBW in the study area. Data were generated from two randomly selected urban hospitals and three rural maternity centres, where a total of 7,012 cases of LBW deliveries with fairly complete antenatal records were extracted. The data were analyzed using SPSS package. The overall incidence of LBW from the study was 16.8%. LBW incidence was higher among females than male babies (P< 0.005). Mean birth weight for males was 1.74±0.55 kg, and 1.66±0.54 kg for females. A correlation analysis showed that maternal age, parity and height significantly influenced birth weight (P< 0.005). A regression model further showed the percentage contribution of sex of baby (r2= 0.43), maternal height (r2= 0.41) maternal age (r2= 0.27) and parity (r2= 0.09) to observed LBW incidence. Adolescent nutrition and reproductive health behaviours, maternal malnutrition for improved pregnancy outcomes and reversal of negative implications of LBW incidence in Nigeria, must be effectively addressed.