OBJECTIVE To determine the efficacy of etoricoxib in the treatment of primary dysmenorrhea. METHODS Seventy-three women were randomly assigned to receive single oral doses of etoricoxib 120 mg, placebo, or naproxen sodium 550 mg at the onset of moderate to severe pain associated with menses. During 3 consecutive menstrual cycles in this double-blind, 3-period, crossover study, pain intensity and pain relief were assessed over the 24-hour period following dosing, and global ratings of therapy were made at 8 and 24 h after dosing. Tolerability was assessed by spontaneous reports of adverse experiences. RESULTS Etoricoxib 120 mg provided analgesic efficacy superior to placebo for the primary endpoint, total pain relief over 8 h (TOPAR8, p<0.001), and for all secondary endpoints (p<0.050). The analgesic effect of etoricoxib 120 mg over the first 8 h was similar to that of naproxen sodium 550 mg. All treatments were well tolerated. CONCLUSIONS Etoricoxib 120 mg provided rapid and sustained analgesia that was superior to placebo and similar to that of naproxen sodium 550 mg.