The median age for menarche is approximately 12.8 years. However, the range varies widely (from 9.1 to 17.7 years of age). The incidence of primary amenorrhea in the United States is less than 0.1%.

Primary amenorrhea is not considered to have occurred until a girl is beyond age 16 without the onset of menses, if she has undergone other normal changes that occur during puberty. Primary amenorrhea may occur with or without other signs of puberty.

There are multiple causes for primary amenorrhea:

• Normal delay of onset (up to age 14 or 15)
• Drastic weight reduction (resulting from poverty, fad dieting, anorexia nervosa, bulimia, very strenuous exercise, or other cause)
• Congenital abnormalities of the genital system (absence of the uterus or vagina, vaginal septum, cervical stenosis, imperforate hymen)
• Hypoglycemia
• Extreme obesity
• Gonadal dysgenesis
• Chromosomal abnormalities such as Turner's syndrome (XO), or Swyer's syndrome (XY)
• Hypogonadotropic hypogonadism
• Testicular feminization syndrome
• True hermaphroditism
• Chronic illness
• Malnutrition
• Cushing's disease
• Cystic fibrosis
• Congenital heart disease (cyanotic)
• Craniopharyngioma, ovarian tumors, adrenal tumors
• Hypothyroidism
• Galactorrhea
• Adrenogenital syndrome
• Prader-Willi syndrome
• Polycystic ovarian disease
• Congenital adrenal hyperplasia
• Pregnancy