Hypogonadism, usually hypogonadotropic in origin, is the most common nondiabetic endocrinopathy in hereditary hemochromatosis (HH). Early studies, usually evaluating small numbers of patients with advanced HH, report prevalence rates of 10-100%. The clinical presentation of HH has changed in recent years as a result of increased awareness and screening. We assessed the prevalence of hypogonadism in a large group of patients with HH diagnosed in a single center over the past 20 yr, the period of follow-up spanning the time before and after widespread screening was introduced and the HFE gene was recognized. Abnormally low plasma testosterone levels, with low LH and FSH levels, were found in nine of 141 (6.4%) male patients tested. Eight of nine (89%) had associated hepatic cirrhosis; three of nine (33%) had diabetes. Inappropriately low LH and FSH levels were found in two of 38 females (5.2%) in whom the pituitary-gonadal axis could be assessed. This is the largest detailed study of hypogonadism reported in HH. The lower prevalence of hypogonadism compared with other reported series reflects the earlier diagnosis of HH in an unselected group of patients attending a single center. Patients with lesser degrees of hepatic siderosis at diagnosis are unlikely to develop hypogonadism.