Previous studies of the seasonality of testicular torsion have yielded conflicting results. Our goal was to examine this issue in a large emergency department (ED) database. We also hypothesized that seasonal patterns would be similar in younger and older patients.This was a retrospective cohort of ED visits. This study was performed on 20 New Jersey and New York EDs. The subjects are consecutive patients seen by ED physicians from January 1, 1996, to December 31, 2009. The authors identified visits with testicular torsion using International Classification of Disease, Ninth Revision codes. We then determined the number of testicular torsion visits by month, correcting for the total number of days over the study period in each month. We compared the corrected number of visits for the winter (December-February) compared with the summer (June-August) using the Student t test, with α set at 0.05. We also calculated these visits for the older and younger half of the patients. Finally, we determined the correlation between mean monthly testicular torsion visits and ambient temperatures.Of the 8,545,979 visits in the database, 768 (0.009%) had an ED diagnosis of testicular torsion. The median age was 15.5 years (interquartile range, 11.7-20.8 years). We found that testicular torsion visits were 39% (95% confidence interval, 24%-57%) more likely in the winter compared with the summer, and this was similar when the older and younger half of the patients were analyzed separately. The correlation coefficient between mean monthly testicular torsion visits and ambient temperature was r = 0.54 (P = 0.006).Testicular torsion visits are more frequent in the winter than in the summer months.