: The lipids constitute majority of dry weight of mature human brain. From lipids, 35% is comprised of PUFA with long chain (LC-PUFA), especially docosahexaenoic acid (DHA) of n-3 family and arachidonic acid (AA) of n-6 family. Humans are dependent on dietary intake of both AA and DHA. Interestingly, the dietary n-6/n-3 ratio increased considerably during last century. LC-PUFAs play numerous roles in the brain, including structural (forming the physico-chemical properties in the lipid bilayer of cellular membranes) and signaling ones. Moreover, they influence neurogenesis and neurotransmission within the nervous tissue. The metabolites of PUFA modulate immune and inflammatory processes in the brain, oxidative stress as well as its consequences. Of high importance is also their connection with several metabolic factors involved in the proper function of the brain and/or were discovered to play a role in the pathogenesis of neuropsychiatric diseases - melatonin, homocysteine, leptin, and adiponectin. This review gives short view of the metabolism and possible mechanisms of PUFA n-3 action in the brain, and their role in the pathogenesis of psychiatric diseases.