Anthelmintic treatment, which is recommended during pregnancy in areas where there is a high rate of anaemia, needs further investigation. We examined prospectively the association between anthelmintic treatment and maternal anaemia, birthweight, and infant mortality in a study of prenatal supplements, in which women received albendazole twice during pregnancy. Women given albendazole in the second trimester of pregnancy had a lower rate of severe anaemia during the third trimester. Birthweight of infants of women who had received two doses of albendazole rose by 59 g (95% CI 19–98), and infant mortality at 6 months fell by 41% (RR 0·59; 95% CI 0·43–0·82). Antenatal anthelmintics could be effective in reducing maternal anaemia and improving birthweight and infant survival in hookworm-endemic regions.