PURPOSE: The risk factors for acute testicular torsion are poorly understood. Environmental factors have been implicated by some authors and discredited by others. The only previous known study in the United States did not demonstrate any seasonal correlation, although the study was done in a warmer climate. We sought to determine if environmental factors impact the incidence of testicular torsion in our temperate climate conditions with a large differential between the warmest and coldest temperatures. MATERIALS and METHODS: We retrospectively studied patients who were diagnosed with testicular torsion between January 1997 and December 2006. Data regarding weather conditions were collected, including season, temperature, humidity and atmospheric pressure at the time of onset of symptoms. Spearman's rank correlation was performed to assess the relationship between atmospheric temperature and frequency of testicular torsion. Multivariate analysis was performed to analyze the effect of covariables. RESULTS: A total of 58 children presented with testicular torsion. Mean temperature at onset of symptoms was 6.9C (range -12C to 23C). Of the patients 81% had symptom onset when the atmospheric temperature was less than 15C. Seasonal incidence of testicular torsion was 36.2%, 31%, 19% and 13.8% for spring, winter, summer and fall, respectively. Spearman's rank correlation test revealed a significant negative correlation between the incidence of testicular torsion and increasing temperature (r = -0.94, p <0.0001) and decreasing humidity (r = -0.44, p <0.001). After controlling for effects by patient age, atmospheric pressure and humidity by multivariate analysis a significant correlation was observed between testicular torsion and decreasing atmospheric temperature. None of the other atmospheric factors examined correlated with the incidence of testicular torsion. CONCLUSIONS: An increased incidence of testicular torsion is seen with decreasing atmospheric temperature and humidity, suggesting a possible etiological role.