Previous studies offer suggestive, but not definitive, evidence that total fat or specific fats may increase prostate cancer risk. This study investigates associations of dietary fat, meat, and dairy foods with prostate cancer risk among 12,025 men in the Carotene and Retinol Efficacy Trial (CARET). After 11 y of follow-up, 890 incident prostate cancers were reported and confirmed. Diet was assessed by a biannual FFQ. Cox proportional hazards models were used to estimate multivariate-adjusted hazard ratios (HR) of intake of fat and fat-related foods (meat and dairy) with prostate cancer incidence. Multiplicative interaction terms tested whether associations differed by family history, race, or smoking. Overall, fat was not associated with total, nonaggressive or aggressive prostate cancer. In subgroup analyses the HR for men with a family history of prostate cancer were 2.47 (95%CI = 0.96-6.37) and 2.61 (95% CI = 1.01-6.72) for total polyunsaturated fat (PUFA) and (n-6) PUFA for the 4th vs. 1st quartiles of intake, respectively. Red meat was not associated with total or aggressive prostate cancer. However, higher dairy intake had a statistically significant reduced risk of aggressive prostate cancer than lower dairy intake (HR = 0.59, 95% CI = 0.40-0.85). Dairy foods also protected current, but not former, smokers against aggressive cancer (HR = 0.42, 95% CI = 0.25-0.70). Our findings suggest that associations of dietary fat with prostate cancer risk may vary by type of fat or fat-containing food, and that risk may vary by host factors, including family history and smoking.