A randomized study was performed on 24 patients with ankylosing spondylitis to compare the efficacy and tolerability of 20 mg tenoxicam daily with 50 mg diclofenac twice daily. There were 6 withdrawals from the group taking tenoxicam and 4 from the diclofenac group. Depression in 1 patient taking tenoxicam was the only significant adverse event. Both drugs were otherwise well tolerated. Tenoxicam and diclofenac were rated as good or excellent by 27% and 55% of patients, respectively. Global assessment, pain and duration of morning stiffness were improved with both drugs but this improvement was not statistically significant and there was no statistically significant difference between the two groups. This study confirms that tenoxicam is effective and well tolerated but larger numbers would be required to detect a small difference between groups.