Dementia such as Alzheimer's disease (AD) is a growing health problem in aging populations in many countries around the world. Currently, there is no cure for AD; consequently, alternative therapies are urgently needed. Recent studies suggest that nutritional intervention may have therapeutic benefits for AD. Specifically, an increased intake of n-3 polyunsaturated fatty acids (PUFA) from fish and marine oils may lower AD risk. This review will summarize the current body of knowledge regarding the association between n-3 PUFA and AD, including human studies and experimental models, and potential mechanisms of action.