Puberty is the complex process of physical changes that occur in an adolescent's body that result in adult secondary sexual characteristics occurring from the maturation of the hypothalamic-pituitary-gonadal (HPG) axis. Onset of puberty is considered delayed when the first physical pubertal changes (secondary sexual characteristics) do not appear by the normally expected age: breast development in girls by age 12-13 years and testicular enlargement in boys by age 14 years. Pubertal delay also encompasses abnormally slow or incomplete progression of expected pubertal changes. For female patients, this is failure to menstruate by age 15-16 years, or more than 3-4 years between thelarche and menarche. For male patients, this is more than 5 years between initial testicular enlargement and completion of puberty. Pubertal delay, which affects 2%-4% of the adolescent population, is a common cause of referral to a pediatric endocrinologist.

There are numerous diverse etiologies for pubertal delay. The causes can be divided broadly into 3 categories: hypogonadotropic hypogonadism (permanent or transient), hypergonadotropic hypogonadism, and other causes.

Common causes in female patients:

• Low body weight / fat, excessive exercise, anorexia nervosa – Low luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
• Constitutional delay of puberty and growth due to chronic disease such as thyroid disease, celiac disease, inflammatory bowel disease (Crohn disease, ulcerative colitis), cystic fibrosis, sickle cell disease, and severe persistent asthma.
• Primary ovarian insufficiency (hypergonadotropic hypogonadism) – High LH, FSH, and gonadotropin-releasing hormone (GnRH) but low estrogen.
• Hypopituitarism (hypogonadotropic hypogonadism) – Usually associated with growth failure.
• Turner syndrome (hypergonadotropic hypogonadism) – Short stature, webbed neck, wide-spaced nipples, and cystic hygroma.
• Genetic disorders – Prader-Willi syndrome, Laurence-Moon-Biedl syndrome, CHARGE syndrome, and Gordon syndrome.

Common causes in male patients:

• Constitutional growth delay is the most common cause (60%) and includes delayed bone age often correlating with current height, short stature, or falling height percentage for age (often called a "late bloomer").
• Gonadal failure (hypergonadotropic hypogonadism) – Low testosterone and increased LH, FSH, and GnRH that results from infection (eg, mumps orchitis), testicular torsion, cryptorchidism, or Klinefelter syndrome.
• Chronic disease – Thyroid disease, celiac disease, inflammatory bowel disease, cystic fibrosis, sickle cell disease, or severe persistent asthma.
• Hypopituitarism (hypogonadotropic hypogonadism) – Usually associated with growth failure.
• Kallmann syndrome – Associated with anosmia, brain tumor, Prader-Willi syndrome, Laurence-Moon-Biedl syndrome, CHARGE syndrome, and Gordon syndrome.