Sixty-four women with primary dysmenorrhea participated in a double-blind, parallel trial of naproxen sodium versus placebo during three menstrual cycles. Comparative measures employed to assess the efficacy of the medications included changes in pain intensity during each dysmenorrheic episode, the degree of pain relief afforded, the necessity of using a supplementary analgesic, and the extent to which medication enabled the patients to continue their daily activities unimpeded. By these measures, naproxen sodium was significantly superior as compared to the placebo. Particularly striking was the fact that of 22 naproxen sodium treated women who historically had to stay at home from work and/or in bed, only 5 remained incapacitated compared with 21 of 26 patients of the placebo group. Only 1 patient experienced side effects (nausea and hypomenorrhea) from naproxen sodium.