Primary amenorrhea (PA) describes the complete absence of menses by the age of 15 years. It is a devastating diagnosis that can affect the adolescent’s view of her femininity, sexuality, fertility and self-image. A normal menstrual cycle can occur only in the presence of: a properly functioning hypothalamus–pituitary axis, well-developed and active ovaries, outflow tract without abnormalities. Any dysfunction in any of these players can result in amenorrhea. PA evaluation includes the patient’s medical history, physical examination, pelvic ultrasonography and initial hormone evaluation, limited to the serum-follicle-stimulating hormone (FSH) and luteinizing hormone, testosterone and prolactin. A karyotype should be obtained in all adolescents with high FSH serum levels. The main causes of PA, whether or not accompanied by secondary sexual characteristics, include endocrine defects of the hypothalamus–pituitary–ovarian axis, genetic defects of the ovary, metabolic diseases, autoimmune diseases, infections, iatrogenic causes (radiotherapy, chemotherapy), environmental factors and Müllerian tract defects. PA management depends on the underlying causes. Estrogen replacement therapy at puberty has mainly been based on personal experience. PA can be due to endocrine, genetic, metabolic, anatomical and environmental disorders that may have severe implications on reproductive health later in life. In some complex cases, a multidisciplinary team best manages the adolescent, including a pediatrician endocrinologist, gynecologist, geneticist, surgeon, radiologist, and psychologist.