The birthweights of 768 singleton neonates were assessed in a study carried out over a 3-year period among indigenous, paturient women in Freetown, where malaria is mesoendemic. About 18.5% of placentae were found infected with malaria and the dominant species was Plasmodium falciparum. The proportion of low birthweight (LBW) babies from infected placentae (22.5%) was significantly greater than the proportion from the uninfected (P < 0.01) and, among the infected, the proportion from primiparae (38.9%) was significantly greater than that from the multiparae P < 0.05). The mean weight of babies from infected mothers was 265 g lower than that of babies from uninfected mothers (P < 0.001) and the babies of primiparae were, on average, 156 g lighter than those of the multiparae (P < 0.001). Although infection significantly lowered mean birthweight in both parity groups (P < 0.001), the reduction was larger in the primiparae (294 g) than in the multiparae (240 g). The LBW risk ratio for primiparae compared with multiparae was 2.3 for both infected and uninfected groups. The proportions of attributable risk indicated that parity accounted for about 57% of all cases of LBW in primiparae, irrespective of infection. Infection enhanced the risk of producing LBW babies in the primiparae by 11.6%. LBW frequency and relative risk were inversely related to parity of mothers and were higher for infected placentae.