To study the therapeutic effects of a single 40 mg intramuscular dose of piroxicam versus a single 75 mg intramuscular dose of diclofenac sodium for treatment of acute renal colic. - The study comprised 64 patients (52 men and 12 women, mean age 28 years, range 18 - 42) who presented with acute renal colic and were diagnosed by IVU, a general urine examination and ultrasonography. The patients were randomly assigned to receive either 40 mg of piroxicam i.m (34 patients) or 75 mg of diclofenac sodium i.m (330 patients). The severity of pain was assessed on Visual Analogue Scale. - Results showed that thirty-two patients (94.1%) markedly improved within 1h of receiving piroxicam and 26 patients (86.6%) improved within 1h of receiving diclofenac sodium (P <0.05). Within 30 min, 25 patients (73.5%) markedly improved after piroxicam and 15 patients (50%) markedly improved after diclofenac sodium (P <0.05). After piroxicam, none of the patients showed pain relapse over a period of 24 h while 9 patients had relapse within 24 h after their initial response to diclofenac sodium. No side effects were reported with use of either treatment. - We concluded that piroxicam can be used successfully to treat acute renal colic and it has earlier onset of action and prolong effect as compared with diclofenac sodium.