The position of the testes reduces their temperature but makes them vulnerable to trauma. Patients with testis cancer frequently report prior testicular trauma, but this trauma may have triggered diagnosis of the tumor rather than been aetiological. In this study, the frequencies of various prior traumatic and temperature exposures in 259 patients with testis cancer were compared with their frequencies in two sets of control patients who did not have testis cancer. Particular effort was made to prevent bias. Testis cancer was not significantly associated with any temperature or trauma exposure and the confidence limits of the findings excluded substantially raised risks. The evidence suggests that raised temperatures and traumas commonly encountered in everyday life are not important risk factors for testis cancer. The possible aetiological roles of extreme trauma sufficient to cause atrophy, and of the trauma and raised temperature which can occur in cryptorchidism, however, need investigation by other methods.