Data from the 1988 National Maternal and Infant Health Survey were used to examine whether regular use of multivitamin/mineral supplements could modify the relation between maternal smoking and fetal death. Maternal smoking was defined as the self-reported average number of cigarettes smoked after recognition of pregnancy. Regular supplement use was defined as use of multivitamin/mineral supplements for at least 3 days per week during the 3 months before and/or after recognition of pregnancy. The sample comprises 12,465 singleton pregnancies, including 9,402 livebirths and 3,063 fetal deaths. Odds ratios were derived from logistic regression analyses after adjustment for a number of demographic and reproductive variables. Major findings are that 1) smoking increased the risk of fetal death; 2) regular supplement use either before or after recognition of pregnancy did not affect the risk of fetal death in the absence of maternal smoking; 3) odds ratios for fetal death among smoking women who regularly used supplements were generally smaller than those for women who did not regularly use supplements but who smoked a comparable number of cigarettes; and 4) a significant negative excess risk due to interaction was observed among women who regularly used supplements before recognition of pregnancy and smoked 20 or more cigarettes a day. These findings suggested that regular multivitamin/mineral supplement use might reduce the risk of fetal death associated with maternal smoking.