Hypogonadotropic hypogonadism (HH) is defined as delayed or absent pubertal development due to impaired gonadotropin secretion. Individuals with idiopathic HH (IHH) usually present with incomplete or absent pubertal development. Over 90% of females with IHH present with primary amenorrhea. Males may have cryptorchidism, testicular atrophy, and microphallus. During childhood, individuals with IHH may have a eunuchoid body habitus (i.e., an arm span that exceeds height by > 5 cm). However, gonadotropin deficiency left untreated may ultimately lead to retarded bone maturation, osteopenia, and osteoporosis in adulthood. In the presence of a partial or total loss of smell (hyposmia or anosmia), IHH is referred to as Kallmann syndrome (KS). Approximately 60% of individuals with IHH have a defective sense of smell. Individuals with KS may have hearing loss, synkinesia, and/or cleft lip/palate. Up to 30% of males with KS also exhibit renal agenesis.