The frequency of gonadotroph cell adenomas among all unselected pituitary adenomas is likely much higher than previously suspected. The prevalence in one series of 139 men with pituitary macroadenomas was 17 per cent (24 per cent if adenomas secreting only alpha subunit are included). The clinical characteristics of patients with gonadotroph cell adenomas are similar. Most are middle-aged men who have a history of normal pubertal development and a normal fertility history and by examination are normally virilized and have testes of normal size. They are brought to medical attention because of visual impairment, which is the result of the enormous size of the adenoma. The most common hormonal characteristics of gonadotroph cell adenomas in vivo is hypersecretion of FSH, which is often accompanied by hypersecretion of FSH-beta and alpha subunits and less often by hypersecretion of LH-beta or intact LH. Another common characteristic is secretion of FSH and/or LH-beta in response to TRH. A few patients with gonadotroph cell adenomas hypersecrete intact LH and therefore have supranormal serum testosterone concentrations. A larger number have secondary hypogonadism, because the adenomas are not secreting intact LH but are compressing the normal gonadotroph cells and impairing LH secretion. These patients have concentrations of intact LH that are not elevated, despite subnormal testosterone concentrations. The testosterone increases markedly in response to human chorionic gonadotropin. Both the clinical and hormonal characteristics of gonadotroph cell adenomas usually make them readily distinguishable from pituitary enlargement due to long-standing primary hypogonadism. Most gonadotroph cell adenomas are now managed first by transsphenoidal surgery to attempt to restore vision as quickly as possible, and then by supervoltage radiation to prevent regrowth of the remaining adenomatous tissue. Surgery usually does improve vision, as well as the pretreatment hormonal abnormalities, and radiation reduces FSH hypersecretion further. Dopamine agonist therapy is experimental but warrants further trial. The hormonal abnormalities detected prior to treatment, such as supranormal basal concentrations of FSH, alpha, and FSH-beta and the FSH and LH-beta responses to TRH, can be used to monitor the response to therapy.