Low birth weight (LBW) and fetal anaemia (FA) are common in malaria endemic areas. To investigate the incidence of infectious morbidity in infants in rural Malawi in relation to birth weight and fetal anaemia, a cohort of babies was followed for a year on the basis of LBW (<2500) and FA (cord haemoglobin < 12.5 g/dl). A matched group of normal birth weight (NBW), non-anaemic (NFA) new-borns were enrolled as controls. Morbidity episodes were recorded at 4-weekly intervals and at each extra visit made to a health centre with any illness. Infants in the NBW NFA group experienced an average of 1.15 (95% C.I. 0.99, 1.31), 1.04 (0.89, 1.19), 0.92 (0.73, 1.11) episodes per year of malaria, respiratory infection and diarrhoea respectively. Corresponding values for the LBW FA group were 0.83 (0.5, 1.16), 0.82 (0.5, 1.16) and 0.76 (0.33, 1.19). FA was not associated with a higher incidence of morbidity, but was significantly associated with a shorter time to first illness episode (p = 0.014). LBW was not a significant risk factor for higher morbidity incidence. LBW and FA were not significant risk factors for incidence of illness episodes in infants.