The current rise in the prevalence of Alzheimer's disease (AD) is unfortunately not matched by new treatment options. In the last 10 years, epidemiological, preclinical and clinical data have enlightened the possible preventive action of omega-3 polyunsaturated fatty acids (n-3 PUFA) in AD and other diseases. While the contribution of recent studies to our general knowledge is priceless, many important new questions have been raised. In the present review, we aim at addressing some of these timely interrogations. First, the transport of n-3 PUFA across the blood-brain barrier is underscored based on preclinical data. Second, the relative contribution of two neuroactive n-3 PUFA found in fish oil, docosahexaenoic acid (DHA; 22:6 n-3) and eicosapentaenoic acid (EPA, 20:5 n-3), remains unclear and is reviewed. Third, clinical trials on neurodegenerative diseases consistently remind us that treating early is critical, and this is likely to be the case with n-3 PUFA in AD as well. Fourth, we draw attention to the possibility that the current knowledge translation approach to make health recommendations might have to be adapted to non-patentable endogenous compounds like n-3 PUFA. We propose that answers to these critical questions will be instrumental toward a rational use of n-3 PUFA in AD.