Male hypogonadism is a clinical syndrome resulting from the body's inability to produce physiological levels of testosterone, sperm, or both.

Clinically, it is categorized by the site of the defect within the hypothalamic-pituitary-gonadal axis. Primary hypogonadism, or hypergonadotropic hypogonadism, occurs when the defect is localized within the testes themselves. In these cases, the pituitary gland attempts to compensate by overproducing luteinizing hormone and follicle-stimulating hormone, yet the Leydig cells remain unresponsive. Common causes include Klinefelter syndrome, mumps orchitis, and testicular trauma.

Secondary hypogonadism, known as hypogonadotropic hypogonadism, stems from a failure of the hypothalamus or pituitary gland to signal the testes to produce testosterone. This results in low testosterone levels accompanied by low or inappropriately normal gonadotropin levels. Etiologies range from congenital conditions like Kallmann syndrome to acquired factors such as pituitary tumors, chronic opioid use, or severe systemic illness. Distinguishing between these two forms is the first critical step in clinical management, as it determines whether the focus of treatment should be purely on testosterone replacement or on addressing a central brain abnormality.