No risk factor other than cryptorchidism has been consistently associated with testicular cancer, and the influence of diet on testicular cancer risk has not been extensively explored. A few studies have found increased testicular cancer risk in men whose diets are high in fat, red meats, and milk or low in fruits and vegetables. We evaluated the relationship of dietary factors and risk of testicular cancer and also examined whether this risk varied by type of testicular cancer. We conducted a hospital-based case-control study at The University of Texas M. D. Anderson Cancer Center (Houston, TX) of 160 testicular cancer cases diagnosed between 1990 and 1996 and 136 friend-matched controls. The results of multivariable logistic regression analysis showed that after adjustment for age, education, income, ethnicity, cryptorchidism, and total daily calories, increasing total fat, saturated fat, and cholesterol consumption were associated with increasing risk of nonseminoma testicular cancer, with odds ratios (ORs) for the highest vs. the lowest quartiles of 6.3, 5.3, and 4.6, respectively. The risk for seminoma testicular cancer marginally increased with increasing intake of total fat and saturated fat, with ORs for the highest vs. lowest quartiles of 1.9 and 2.1, respectively. Higher total fat consumption was nearly significantly related to increased mixed germ cell tumor risk, with an OR for highest vs. lowest quartile of 4.2. This study supports the hypothesis that diet (particularly high fat consumption) increases testicular cancer risk in young men. However, the small sample size and the possibility that these observations may be due to bias indicate that the relationship of diet and testicular cancer risk needs to be further examined within a prospective or incident case-control study.