Many types of dietary supplements have been advocated for the reduction of certain symptoms of premenstrual syndrome (PMS). However, only one supplement-calcium-has been demonstrated to be of significant benefit in a large, rigorous, double-blind, placebo-controlled trial. Limited evidence suggests that magnesium, vitamin E and carbohydrate supplements might also be useful, but additional research is needed to confirm these findings. Trials of vitamin B6 supplementation have had conflicting results, and high doses of this vitamin taken for prolonged periods of time can cause neurological symptoms. Trials of evening primrose oil have also had conflicting results; the two most rigorous studies showed no evidence of benefit. A variety of herbal products are suggested to reduce symptoms of PMS. The efficacy of these products is uncertain because of a lack of consistent data from scientific studies. Health professionals should be aware of the possible use of these supplements and ask those with PMS about their use of such products and counsel them based upon the totality of evidence.