Prostate cancer is the most common malignancy in men in the United States, with substantially higher rates among American blacks than whites. We carried out a population-based case-control study in three geographic areas of the United States to evaluate the reasons for the racial disparity in incidence rates. A total of 932 men (449 black men and 483 white men) who had been newly diagnosed with pathologically confirmed prostate cancer and 1201 controls (543 black men and 658 white men) were interviewed in person to elicit information on potential risk factors. This report evaluates the impact of dietary factors, particularly the consumption of animal products and animal fat, on the risk of prostate cancer among blacks and whites in the United States. Increased consumption (grams/day) of foods high in animal fat was linked to prostate cancer (independent of intake of other calories) among American blacks [by quartile of intake, odds ratio (OR) = 1.0 (referent), 1.5, 2.1, and 2.0; P(trend) = 0.007], but not among American whites [by quartile of intake, OR = 1.0 (referent), 1.6, 1.5, and 1.1; P(trend) = 0.90]. However, risks for advanced prostate cancer were higher with greater intake of foods high in animal fat among blacks [by quartile of intake, OR = 1.0 (referent), 2.2, 4.2, and 3.1; P(trend) = 0.006] and whites [by quartile of intake, OR = 1.0 (referent), 2.2, 2.6, and 2.4; P(trend) = 0.02]. Increased intake of animal fat as a proportion of total caloric intake also showed positive but weaker associations with advanced prostate cancer among blacks (P(trend) = 0.13) and whites (P(trend) = 0.08). No clear associations were found with vitamin A, calcium, or specific lycopene-rich foods. The study linked greater consumption of fat from animal sources to increased risk for prostate cancer among American blacks and to advanced prostate cancer among American blacks and whites. A reduction of fat from animal sources in the diet could lead to decreased incidence and mortality rates for prostate cancer, particularly among American blacks.