Fatty acids comprise a large family of compounds possessing diverse chemical structures and biological activities. Among various fatty acids, omega-3 and omega-6 ones are necessary for human function and they should be supplemented, particularly omega-3 acids, because of their insufficient synthesis in an organism. The characteristics of such compounds, including their chemical structure and function, will be discussed, taking into account the presence or absence of double bond/s localized to specific place/s of fatty acid carbon chain, which determines their unsaturated or saturated nature. A focus will be given to docosahexaenoic acid (DHA) – a polyunsaturated fatty acid that is an indispensable building and functional element of the central nervous system. Insufficient supply of DHA, as well as another omega-3 fatty acid – eicosapentaenoic acid (EPA), may contribute to various membrane and cell dysfunctions and pathologies, including inflammation and neurodegeneration. These fatty acids, especially DHA, are crucial for early development, e.g. neurogenesis and synaptogenesis, and later processes such as cognitive brain development. On the other side, DHA and EPA, possessing in their structures respectively 6 and 5 intracarbon double bonds, are particularly sensitive – especially under insufficient antioxidant defense – to peroxidation and generation of reactive oxygen species, structural defragmentation, and formation of immunogenic conjugates with proteins. Analysis of possible „pros” and „cons” related to supplementation with omega-3 fatty acids (diet, pharmaceuticals) indicates a clear advantage of the former, which suggests that intake with either food or supplements rich in DHA and EPA may be a reasonable prophylactic-therapeutic strategy useful in combating various ailments of our organism, including disorders of the central nervous system.