Obesity, the result of combined genetic and environmental factors, is in recent decades one of the most frequent diseases and is encountered mainly in Europe and North America. In women it is associated with the risk of several diseases, such as diabetes mellitus, osteoarthritis, cardiovascular diseases, sleep apnoea syndrome, breast cancer, cancer of the uterus and also with impairment of reproductive functions. Already during the last century some observations confirmed that a very low or very high body weight is more frequently associated with disorders of the menstrual cycle (MC), infertility and poor reproductive capacity. However only during the last decades the pathophysiological and molecular mechanisms of this relationship were gradually elucidated. The main factors which influences the menstrual cycle in obesity are: impaired estrogen metabolism, changes in the concentration of sex hormone binding globulin, hyperinsulinaemia, and probably also leptin levels.

        Key words: Obesity - Disorders of the menstrual cycle - Polycystic ovaries syndrome - Hyperinsuli- naemia - Insulin resistance - Hyperandrogenism - Metformin