Background: Diet is an important lifestyle factor that may prevent or slow the onset and progression of neurodegeneration. Some, but not all, recent studies have suggested that adherence to a healthy dietary pattern may be associated with reduced risk of dementia. Objective: In this meta-analysis, we systematically examined the associations between overall dietary patterns, assessed a priori and a posteriori, and risk of dementia. Methods: We systematically searched PubMed, Web of Science, and the Cumulative Index for Nursing and Allied Health databases from January 1, 1981 to September 11, 2019. Prospective studies published in English were included. Random-effects model was used to calculate the pooled risk ratios and 95% confidence intervals (CIs). Results: Sixteen research articles were identified in the systematic review and 12 research articles including 66,930 participants were further included for the meta-analysis. Adherence to high diet quality or a healthy dietary pattern was significantly associated with lower risk of overall dementia (pooled risk ratio = 0.82; 95% CI: 0.70, 0.95; n = 12) and Alzheimer's disease (pooled risk ratio = 0.61; 95% CI: 0.47, 0.79; n = 6) relative to those with low diet quality or an unhealthy dietary pattern. Subgroup analyses stratified by age, sex, follow-up duration, diet quality assessment approach, study location, and study quality generated similar results. Conclusion: Adherence to a healthy dietary pattern was associated with lower risk of overall dementia. Further randomized controlled trials are needed to provide additional evidence about the role of a healthy diet on the development and progression of dementia. Keywords: Alzheimer’s disease; dementia; diet quality; dietary pattern.