Background: Kidney stones are a fairly common problem that manifests itself as symptoms of acute abdominal and flank pains in patients presenting to emergency departments. Objective: The present study was conducted to compare the analgesic effect of intravenous fentanyl with that of intranasal ketamine in renal colic patients. Methods: One mg/kg of intranasal ketamine was administered in the first group, and one mu g/kg of intravenous fentanyl in the second group. The pain severity was measured in the patients in terms of a visual analogue scale (VAS) score at the beginning of the study and at minutes 5, 15 and 30, and the medication side-effects were evaluated and recorded. Results: A total of 130 patients were ultimately assessed in two groups of 65. In the ketamine group, the mean severity of pain was 8.72 +/- 1.52 at the beginning of the study (P < 0.001), 5.5 +/- 2.97 at minute 5 (P < 0.001), 338 = 3.35 at minute 15 (P= 0.004) and 253 +/- 3.41 at minute 30 ( P = 0.449). In the fentanyl group, this severity was 9.66 +/- 88.8 in the beginning of the study (P< 0.001), 727 +/- 1.37 at minute 5 (P< 0.001), 4.61 = 1.5 at minute 15 (P = 0.004) and 1.24 +/- 1.25 at minute 30 (P= 0.449).The general prevalence of the medication sideeffects was 10 (15.4%) in the ketamine group and 1 (1.5%) in the fentanyl group (P = 0.009). Conclusions: Ketamine was found to be less effective than fentanyl in controlling renal colic-induced pain, and to be associated with a higher prevalence of side-effects: nevertheless, ketamine can be effective in controlling this pain in conjunction with other medications. (C) 2019 Elsevier Inc. All rights reserved.