Objective  To assess the possible therapeutic effect of 40 mg sublingual piroxicam (fast‐dissolving dosage form, FDDF) compared with intramuscular 75 mg diclofenac, as a reference drug, on acute renal colic in a randomized, double‐blind controlled clinical trial. Patients and methods  Eighty patients were assigned to one of two treatment groups; one received an intramuscular injection with 0.2 mL distilled water and two sublingual tablets of 20 mg piroxicam FDDF, and the other received an intramuscular injection with 75 mg diclofenac sodium and two sublingual tablets of placebo. Pain intensity was evaluated by the patient using a visual analogue scale and by the observers. Vital signs at baseline and 30 min after the administration of the study drugs were also recorded. Results  The overall efficacy of the treatment was 81%; nine patients in the piroxicam and six in the diclofenac group (no significant difference) required rescue treatment. Compared with baseline levels, the pain relief was significant (P<0.001) at 30 min in both groups. Twenty‐two patients in the piroxicam and 25 in the diclofenac group attained complete pain relief at 30 min, as evaluated by the observer (no significant difference). Both treatments were similarly effective in decreasing vital signs, mainly systolic blood pressure, heart and respiratory rates. However, when the percentage change was compared between the groups, piroxicam significantly decreased the respiratory rate (P<0.03). Conclusion  Piroxicam FDDF is as effective as parenteral diclofenac in emergency renal colic treatment. Furthermore, its ease of self‐administration increases patient compliance and potential use in general practice.