Polyunsaturated fatty acids (PUFA) play a crucial role in cerebral structure and function. Omega-3 PUFA is an exciting area of research, with docosahexaenoic acid (DHA) emerging as a new potential agent for prevention of cognitive decline and treatment of Alzheimers disease. Preclinical studies suggest that DHA maintains membrane fluidity, improves synaptic and neurotransmitter functioning, enhances learning and memory performances and displays neuroprotective properties. Several epidemiological studies supported the association between Omega-3 PUFA consumption and a lower prevalence of dementia. Although data are divergent, a growing body of evidence supports the view that regular consumption of dietary fish and seafood (which are rich in omega-3 PUFA) prevents cognitive decline. Finally, at present, few data are available from randomized clinical trials (RCTs). on the association between cognition and Omega-3. Ongoing RCTs that assess the effect of Omega-3 might provide new evidence on prevention and treatment of dementia. In this review, we summarize preclinical and clinical research suggesting that DHA exerts beneficial effects on cognitive function with ageing.