OBJECTIVE We have conducted a clinical trial to compare the pain-relieving effect and safety of diclofenac administered intramuscularly to indomethacin given intravenously. METHODS The study was designed as a randomized single-blind trial. It was carried out at Oslo Emergency Hospital (outpatient setting or stay < 24 h). 41 patients with a mean age of 41.6 years received 75 mg diclofenac and 42 patients with a mean age of 45.2 years were given 50 mg indomethacin. The two groups were similar in regard to baseline characteristics except gender distribution. RESULTS Statistically significant reduction in pain intensity was achieved after 5 min in the diclofenac group (p < 0.01), and after 10 min in the indomethacin group (p < 0.01). The probability of having pain after 1 h was 52% in the indomethacin group and 37% in the diclofenac group (p = 0.11). Rescue medication with pethidine after 2 h was given in 9 and 5 patients, respectively. Four patients in the diclofenac group reported one occurrence of adverse effect each, while 9 patients on indomethacin experienced 14 occurrences, mainly dizziness and nausea. CONCLUSIONS These findings together with a simpler mode of administration indicate that diclofenac may be preferred in the analgesic treatment of renal colic.