Prenatal maternal micronutrient supplementation has been suggested as a means to reduce the proportion of low birth weight babies in low-income countries. The effects of prenatal multi-micronutrient supplements on birth weight and perinatal mortality were studied in a randomised controlled trial among 2100 pregnant women in Guinea-Bissau. Women up to 37 weeks pregnant were individually randomised to daily supplements until delivery of identically looking tablets containing 1) Iron (60 mg) + folate (400 µg), 2) One recommended dietary allowance (RDA) of 5 minerals and 10 vitamins, including iron (30 mg) and folate (400 µg), or 3) Two RDA's of 5 minerals and 10 vitamins, including iron (30 mg) and folate (800 µg). Supplements were provided in known excess at fortnightly home visits until delivery. Compliance was assessed by tablet count.