There is evidence of the relation of sex steroid hormones and sexual dimorphism in immune system response to infectious diseases. The aim of this review was to identify the role of sex hormones in immune function and sexual dimorphism of immune reactions. Gonadal hormones together with the immune system play an important role in process of immune responses to the disease [1]. Estrogens, progesterone and testosterone have different impacts on immune cells and different gonadal hormones are of high importance for responses of innate and adaptive immunity [1, 2]. Estrogens mainly enhance immune function while testosterone has a suppressive role. Higher progesterone during pregnancy leads to autoimmune disease remission and an elevated susceptibility toward certain infectious diseases [2, 3, 4]. The intensity and prevalence of viral infections are typically higher in males, whereas disease outcome could be worse for females [5]. Sexual dimorphism of immune function is based on different concentrations of sex hormones in males and females and on a specific mediating role of these hormones in immune function and response along with differences in innate and adaptive immunity.