Objective: The relationship between metabolic syndrome (MS) and hypogonadism has always been investigated in study groups confounded with aging, obesity or chronic metabolic disorders. So far, there has been no data about the presence of MS in young hypogonadal patients. Also, there is controversial data about the metabolic effects of testosterone replacement therapy. We investigated the frequency of MS in treatment-naive, young men with congenital hypogonadal hypogonadism (CHH). We also searched for the effect of testosterone replacement on the metabolic profiles of this specific patient group.