Premature ovarian insufficiency (POI) is a clinical syndrome defined by the presence of ovarian dysfunction before the age of 40 years. The prevalence of POI is around 1%. The following diagnostic criteria are mostly adopted nowadays: (i) oligo/amenorrhea for at least four months, and (ii) FSH levels > 25 IU/l on two occasions more than four weeks apart.|POI can be the result of iatrogenic, genetic and autoimmune causes. Karyotyping should be performed in all women with non-iatrogenic POI, while fragile X premutation testing is also indicated. Screening with anti-21OH Abs (or alternatively adrenocortical Abs) and anti-TPO Abs should also be considered. No causal relationship between smoking and POI has been proved, but smoking has been associated with early menopause. In the majority of cases, the cause of POI is not identified and these women are described as having idiopathic POI.|Untreated POI is associated with increased risk of type 2 diabetes mellitus and reduced life expectancy, largely due to cardiovascular disease. POI is also associated with reduced bone mineral density and increased risk of fracture. These women should maintain a healthy lifestyle with appropriate diet and exercise.|Women with POI should also receive hormone replacement therapy with standard doses of oral (17ß-E2 2-4 mg or CEE 0.625-1.25 mg) or transdermal (17ß-E2 50-100 μg) estrogens and progestogens (natural progesterone 200 mg or dihydrogesterone 10-20 mg or norethisterone 1-5 mg) up to the age of normal menopause (50 years).|There is a small chance of spontaneous pregnancy, therefore women with POI should be advised to use contraception, if they wish to avoid pregnancy. There are no interventions that have been reliably shown to increase ovarian activity and natural conception rates, therefore oocyte donation is, so far, the established option in the event of fertility issues.