Previous epidemiologic studies have generated inconsistent results regarding the associations between fat intakes and risk of Parkinson's disease. The authors investigated these associations in two large, prospective US cohorts. They documented 191 incident cases of Parkinson's disease in men (1986-1998) and 168 in women (1980-1998) during the follow-up. Overall, intakes of total fat or major types of fat were not significantly associated with the risk. The relative risks comparing the highest quintile of animal fat intake with the lowest were 1.42 for men (95% confidence interval (CI): 0.91, 2.20; p for trend = 0.1) and 0.65 for women (95% CI: 0.36, 1.16; p for trend = 0.3). For men, but not women, replacement of polyunsaturated fat with saturated fat was associated with a significantly increased risk (5% of energy intake, relative risk (RR) = 1.83, 95% CI: 1.10, 3.03). Of the individual polyunsaturated fatty acids, arachidonic acid tended to be inversely associated with the risk (pooled RR between extreme quintiles = 0.65, 95% CI: 0.46, 0.91; p for trend = 0.05). Results do not support an important role of overall fat intake in the pathogenesis of Parkinson's disease, but a possible adverse effect of saturated fat for men could not be excluded.