OBJECTIVE: To determine whether renal colic incidence in the temperate environment of Melbourne, Australia, varies with ambient temperature and season. METHODS: This was a retrospective analysis of patients with renal colic who presented, between 1999 and 2005 inclusive, to a Victorian inner city emergency department. The emergency department database was interrogated to identify patients with an International Classification of Diseases 10th revision diagnostic code of renal colic. All weather data were obtained from the Bureau of Meteorology (Melbourne, Australia). The primary study endpoints were renal colic incidence and mean monthly temperature and humidity. Data were analysed using Spearman's correlation coefficient and the normal Z-test. RESULTS: About 3070 cases were identified. Mean age was 45.0 (SD 14.0) years. Males predominated with 2374 (77.3%) cases. For both sexes, renal colic incidence was lower amongst younger and older patients. The summer rate was significantly greater than the winter rate (1.53 vs. 1.24 presentations/day, rate difference 0.29, 95% confidence interval 0.15-0.43, P<0.001). There were significant positive correlations between the mean monthly maximum temperature and the absolute number (R Euro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin) 0.34, P Euro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin) 0.002) and rate (presentations/day, R Euro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin) 0.26, P Euro Surveillance (Bulletin Europeen Sur Les Maladies Transmissibles; European Communicable Disease Bulletin) 0.017) of presentations. The summer/winter ratio of renal colic incidence was not affected by age or sex. CONCLUSION: The incidence of renal colic in the temperate environment increases with sustained increases in ambient temperature and is unaffected by age or sex. Patients at risk of renal colic should increase their fluid intake over the whole of the summer period not just during periods of extreme heat.