OBJECTIVE To compare the prevalence of Renal Colic (RC) in Ramadan (the month of fasting for Moslems) with other months of the lunar year. METHODS Records of 574 subjects, who were admitted in the two medical centers of Varamin (a city in a hot region of Iran), were reviewed in order to estimate the time trend of RC. RESULTS This study included 398 males (69.3%) and 176 females (30.7%). Twenty-seven males (62.8%) and 16 females (37.2%) were admitted in Ramadan; and 371 males (69.9%) and 160 females (30.1%) in other months (p<0.4) of the year. RCs were more common in June (68 patients, 11.8%), July (65 patients, 11.3%) and November (60 patients, 10.5%). Forty-three subjects (7.5%) admitted in Ramadan; the frequency was not significantly different from mean admission of the year (48.3 +/- 17 patients). There was also no significant difference between frequency of admissions in Ramadan and mean admission during cold half of the year (36.8 +/- 18.34 patients, p = 0.3). Mean admission (64.4 +/- 3.3 patients) in warm seasons were significantly higher than Ramadan (p < 0.001). CONCLUSIONS Lack of difference in the two groups indicates that higher temperature rather than fasting as a cause for RCs.