A multi-centre, double-blind, randomised parallel-group study was conducted to compare the efficacy and safety between etodolac SR and diclofenac in treating patients with osteoarthritis of the knee. Thirty-two patients receiving etodolac SR (400 mg/day) and 32 patients receiving diclofenac (100 mg/day) were included for analyses. After receiving the study treatment, etodolac SR and diclofenac were shown to produce comparable improvement in pain relief as measured by a 10-cm visual analogue scale. There was no statistically significant difference observed between groups for the degree of functional impairment or the amount of paracetamol taken. The etodolac SR treatment group showed fewer incidents of adverse event. In addition, fewer gastrointestinal symptoms were observed in the etodolac SR treatment group. A statistically higher percentage of etodolac SR-treated patients were better tolerated to the study treatment compared with the diclofenac-treated patients. Etodolac SR-treated patients also took fewer antacids than the diclofenac-treated patients during the treatment period. In conclusion, etodolac SR is an effective treatment with fewer side-effects than diclofenac for patients with osteoarthritis of the knee.