In a study of 250 cases of cancer of the testis and of neighborhood- and age-matched controls in upstate New York in 1977-1980, the authors found that risk was enhanced by possession of a number of traits associated with exposure of the testis to heat; occupational exposures to fertilizers, phenols, and fumes or smoke; and trauma to the testis. Risk was also increased for characteristics related to congenital and developmental aberrancies and testis-related abnormalities, e.g., low sperm count, fertility problems, atrophic testis, and cryptorchidism. Several of these risk factors were statistically significant in a multiple regression model that adjusted for all other significant traits, age, and education.