The objective of the study was to compare efficacy and safety of Fenbufen and Aspirin in osteoarthritis. The study was a double-blind, randomized trial with crossover. The test subjects were treated for 4 weeks with 600 mg Fenbufen and for 4 weeks with 3.6 g Aspirin per day. 35 patients with osteoarthritis of the knee and 18 patients with osteoarthritis of the hip participated in the study. The physical measurements of osteoarthritis activity showed significant improvement with both Fenbufen and Aspirin. The drugs were comparable with respect to: 1) improvement of physical m-easurements, 2) investigator's assessments, and 3) patients' assessments. A smaller number of patients reported drug-related side effects with Fenbufen than with Aspirin. 57% of the patients reported side effects during treatment with Aspirin and 40% during treatment with Fenbufen. There were no abnormalities discovered in haematologic or biochemical tests performed during the course of the trial.