The efficacy and safety of nabumetone (1,000 mg at bedtime) and naproxen (250 mg twice daily) were compared in a six-month, randomized, double-blind study of patients with osteoarthritis. Forty patients were entered in the study and completed a washout phase, and 37 were evaluable for efficacy. Of these, 18 patients received nabumetone and 19 received naproxen. Both treatment groups had significant improvement from baseline in all of the efficacy variables measured. All 40 patients were evaluated for safety. Fifty percent of the patients treated with nabumetone and 65 percent of the patients treated with naproxen had at least one drug-related or unknown-related adverse experience. Fifteen percent of patients in both groups had treatment-related adverse experiences that were moderate or severe. There were no statistically significant differences in the two treatment groups with regard to efficacy or adverse experiences.