Primary dysmenorrhea, menstrual cramps in otherwise well women, produces mild to debilitating cramping of the uterus. More than half, and by some estimates 90% of all American women experience menstrual cramps during the first several days of menstruation. About one in ten women are unable to perform their normal routine for one to three days each menstrual cycle due to severe uterine cramping. Although the uterus contracts and relaxes routinely, during menstruation the contractions are much stronger producing pain and "cramps". Women with dysmenorrhea have high levels of prostaglandins, hormones believed to cause menstrual cramping. Prostaglandins are believed to temporarily reduce or stop blood supply to the uterus, thus depriving the uterus of oxygen resulting in contractions and pain. One would expect zinc, like the non-steroidal anti-inflammatory drugs used to treat cramping, to reduce the production of prostaglandins. Zinc inhibits the metabolism of prostaglandins ruling out this mechanism of action, suggesting erroneously that zinc deficiency would prevent cramping. However, it is shown by case histories that zinc, in 1-3 30-mg doses given daily for one to four days prior to onset of menses, prevents essentially all to all warning of menses and all menstrual cramping. One hypothesis for a mechanism of action is that a precursor (COX-2) or metabolite of prostaglandins causes menstrual cramping and not prostaglandins themselves. Another hypothesis is that zinc has antioxidant and anti-inflammatory actions in the uterus. Improvement in micro-vessel circulation by zinc may help prevent cramping and pain. In patients consuming 31 mg of zinc per day, premenstrual tension (PMT) symptoms did not occur, while in patients consuming 15 mg of zinc, PMT symptoms did occur (P<0.001). Protocols using 30 mg of zinc once to three times a day for one to four days immediately prior to menses to prevent dysmenorrhea are described and they are recommended for additional study. The side effect from the absence of all warning of pending menses due to zinc treatment was concern of possible pregnancy. The United States RDA for zinc appears to be too low to optimize women's health and prevent menstrual cramps.