Ramadan fasting for Muslims means abstinence from eating, drinking, and smoking from sunrise to sunset. There are concerns whether the occurrence of renal colic increases during the month of Ramadan. In view of the importance of fasting among Muslims, the occurrence of renal colic during Ramadan fasting has been compared during the following periods: two weeks before commencement of Ramadan (stage-1), during the first two weeks (stage-2), the last two weeks (stage-3), and, two weeks after Ramadan (stage-4). This was a prospective observational study, which was carried out in patients with symptoms of renal colic who were referred to the emergency wards in two major hospitals in Iran. During the study period, 610 subjects were admitted with renal colic during the four periods of study; there were 441 males (72.3%) and 169 females (27.7%). The number of patients with renal colic was highest during the first two weeks of Ramadan in comparison with the other periods (stage-1: 157, stage-2: 195, stage-3: 139, stage-4: 119, P < 0.05]. Results from this study show that the number of admissions due to renal colic was high during the first two weeks of Ramadan. However, the number of admissions decreased during the last two weeks of Ramadan and this trend continued after Ramadan.