Nutrient requirements increase during periods of growth and development such as pregnancy and lactation. In response, many clinicians recommend dietary supplements during these important periods of the life cycle. Although there exist some recommendations concerning the need for a limited number of nutrients in supplemental form (eg, iron, folic acid, and iodine), there is a relative paucity of data concerning the use of dietary supplements during pregnancy and lactation. Limited data suggest, however, that usage is dependent on demographic, sociologic, and economic factors. Thus, it is possible that the nation's most at-risk populations may be those who are least likely to comply with these recommendations. As researchers continue to study what is meant by "optimal nutrition" during pregnancy and lactation, it is likely that additional recommendations concerning dietary supplements will emerge. For example, it is possible that increased consumption of some of the long-chain polyunsaturated fatty acids during pregnancy or lactation may impart a benefit to infant health. Understanding better the population dynamics related to supplement use during these periods will be critical in implementation of campaigns designed to encourage appropriate use--and discourage inappropriate use--of dietary supplements during these important phases of human reproduction. The purpose of this article is to briefly review what is known about the use of dietary supplements in North America and, more specifically, in pregnant and lactating women. In addition, information concerning barriers to supplement use is discussed as are current recommendations for dietary supplement consumption during these periods of the life cycle.