The aim of this article was to present a simple classification of phytoestrogens, their approximate content in food products as well as their synthesis, biotransformation and activity in human organism. Having various mechanisms of action, phytoestrogens display both beneficial and adverse effects on physiological processes. Several positive health effects have been associated with phytoestrogens, such as a protective role against the development of cancers, proestrogenic effects (particularly with postmenopausal women) and beneficial influence on cardiovascular and osseous systems. Adverse effects of phytoestrogens have been observed in fetuses and young specimens. Limited studies have displayed disorders in morphology and physiology of the male reproductive system. High plasma phytoestrogens level inhibits a cellular activity of some enzymes, e.g. enzymes involved in the synthesis of steroid hormones. Direct contact with exogenous, environmental estrogens depends on human diet and it can be variable in different populations.