Meloxicam is a new nonsteroidal anti-inflammatory drug (NSAID), which, in animal tests, displays a high potency for anti-inflammatory and analgesic action. The aim of this study was to investigate the efficacy and tolerability of 15 mg meloxicam in comparison with 100 mg slow-release diclofenac in patients with osteoarthritis of the knee. Two hundred and fifty-eight patients were included in the intent-to-treat analysis; these were randomized into two groups to receive either 15 mg meloxicam (N = 128) or 100 mg diclofenac (N = 130) for a period of 6 weeks. The results with respect to efficacy showed a trend in favor of meloxicam regarding pain on movement, global efficacy and paracetamol consumption, although these differences did not reach statistical significance. The most frequently-occurring adverse events in both groups were of a gastrointestinal (GI) nature. However, there was a higher incidence (26 vs 16%) of GI adverse events in the diclofenac group compared with the meloxicam group. Both drugs were well tolerated when assessed by the patients on a visual analog scale (VAS). Thus, 15 mg meloxicam is an effective and well-tolerated therapy for osteoarthritis and compares favorably with diclofenac 100 mg, a well-established treatment for this indication.