This study assesses the association between intake of protein, fats, cholesterol, and carbohydrates and the risk of prostate cancer (PCa). Between 1994 and 1997, in 8 Canadian provinces, mailed questionnaires were completed by 1,797 incident, histologically confirmed cases of PCa and 2,547 population controls. Information was collected on socioeconomic status, lifestyle habits, and diet. A 69-item food frequency questionnaire provided data on eating habits 2 yr before the study. Odds ratios (ORs) and 95% confidence intervals (CIs) were computed using unconditional logistic regression, including terms for sociodemographic factors, body mass index, alcohol, and total energy intake. Intake of trans fat was associated with the risk of PCa; the OR for the highest vs. the lowest quartile was 1.45 (95% CI = 1.16-1.81); the association was apparently stronger in subjects aged less than 65, normal weight men, and ever smokers. An increased risk was also observed with increasing intake of sucrose and disaccharides. In contrast, men in the highest quartile of cholesterol intake were at lower risk of PCa. No association was found with intake of total proteins, total fat, monounsaturated fats, polyunsaturated fats, monosaccharides, and total carbohydrates. The findings provide evidence that a diet low in trans fat could reduce PCa risk.