This study investigates the association between dietary fat intake and the risk of incident dementia in the Rotterdam Study, a population-based prospective cohort. The study included 5,386 participants aged 55 years or older, assessed at baseline with a semiquantitative food-frequency questionnaire. Dementia was diagnosed using a three-step protocol, including clinical examinations. After adjusting for age, sex, education, and energy intake, high intakes of total fat, saturated fat, and cholesterol were associated with an increased risk of dementia, particularly dementia with a vascular component. Fish consumption, a source of n-3 polyunsaturated fatty acids, was inversely related to the risk of dementia, especially Alzheimer's disease (AD). The findings suggest that high saturated fat and cholesterol intake increases the risk of dementia, while fish consumption may reduce this risk. The study highlights the importance of dietary factors in the prevention of dementia and provides insights into the potential mechanisms underlying these associations.This study investigates the association between dietary fat intake and the risk of incident dementia in the Rotterdam Study, a population-based prospective cohort. The study included 5,386 participants aged 55 years or older, assessed at baseline with a semiquantitative food-frequency questionnaire. Dementia was diagnosed using a three-step protocol, including clinical examinations. After adjusting for age, sex, education, and energy intake, high intakes of total fat, saturated fat, and cholesterol were associated with an increased risk of dementia, particularly dementia with a vascular component. Fish consumption, a source of n-3 polyunsaturated fatty acids, was inversely related to the risk of dementia, especially Alzheimer's disease (AD). The findings suggest that high saturated fat and cholesterol intake increases the risk of dementia, while fish consumption may reduce this risk. The study highlights the importance of dietary factors in the prevention of dementia and provides insights into the potential mechanisms underlying these associations.