Premature ovarian insufficiency (POI), is a clinical syndrome defined by amenorrhea due to loss of ovarian functioning before the age of 40, that affects 1% of the female population. The definition of premature ovarian insufficiency is important in clinical practice to enable distinguishing between POI and physiological menopause. Females with POI, other than suffering from lack of oestrogen, are more likely to develop osteoporosis and cardiovascular diseases. Due to cessation of ovulation and loss of fertility, women also face psycho – social issues that considerably affect their quality of life. Symptoms of POI are similar to those that affect women in menopause. POI can be caused by chromosomal and genetic anomalies, metabolic diseases, autoimmune disorders, infections, iatrogenic causes, but in most cases the cause is unknow. Late diagnosis or nontreatment of POI is closely related with the increasing number of females that cannot achieve pregnancy. Criteria for diagnosing POI in females younger than 40 years old with 4 to 6 months of amenorrhea, oligomenorrhea or other dysfunctional bleedings, involves laboratory tests: human karyonic gonadotropin, FSH, TSH, oestradiol and prolactin. POI carries a high risk of infertility, osteoporosis, cardiovascular diseases and premature death. Symptoms, as well as risk reduction, could be improved by applying hormonal replacement therapy (HRT). HRT replaces the lack of estrogen and progesterone and is considered to be the golden standard in the treatment of POI