Premature ovarian insufficiency can be defined as cessation of ovarian function in women younger than 40 years old and is linked to the development of hypergonadotropic hypogonadism. Generally, the incidence of POI is estimated as 1% of women. Specifically, it can be stated that it occurs in 1% of women younger than 40 years old and in 0.4% in women aged less than 35 years old. The detailed epidemiological data regarding POI is very limited. Pathogenesis of POI is very complex and still not fully understood. Genetic causes are regarded as leading pathomechanism of POI. Other causes are referred to autoimmune, metabolic, and infectious background. Due to oncological treatment of adolescents and young women, iatrogenic actions constitute essential part of POI causes. Idiopathic cause of POI still requires elucidation. In patients with spontaneous POI, amenorrhea or oligomenorrhea may be accompanied by vasomotor symptoms (hot flashes and night sweats), dyspareunia related to vaginal dryness, lack of libido, sleep disturbance, and arthralgia. Symptoms of estrogen deficiency develop in many, but not all, patients. In women experiencing menopause induced by surgery or cancer treatment, the symptoms of estrogen deficiency are often more severe and longer lasting. The strongest evidence of autoimmune mechanisms involvement in pathology of POI comes from the high incidence of coexistence of POI with other autoimmune disorders. It is estimated that around 10–55% of patients with POI have associated autoimmune diseases. The effect of POI-associated estrogen deficiency on bone is the most clearly established adverse consequences of POI condition although hypoestrogenism can be asymptomatic in aspect of bones for many years in most women until fracture occurs. Low bone mineral density (BMD), usually assessed by dual energy X-ray absorptiometry (DEXA), is a risk factor of fracture and widely used as a surrogate in assessing fracture risk and treatment effects. The main reason of shortened life expectancy in POI patients is cardiovascular disease. To date, it has been shown that POI women present several risk factors for the development of cardiovascular disease: endothelial dysfunction, autonomic dysfunction, metabolic disturbances, and increased inflammatory factors. Therefore, early initiated estrogen-progestin replacement therapy is recommended in POI women to treat menopausal symptoms, maintain bone health and prevent osteoporosis, and control the future risk of cardiovascular disease The treatment should be continued at least until the average age of natural menopause.