The investigators sought evidence-based criteria for identifying late-onset hypogonadism in men between the ages of 40 and 79 years on the basis of the association between symptoms and a low testosterone level. The data suggest that late-onset hypogonadism can be defined by the presence of at least three sexual symptoms with a total testosterone level of less than 11 nmol per liter and a free testosterone level of less than 220 pmol per liter. The data suggest that late-onset hypogonadism can be defined by the presence of at least three sexual symptoms with a total testosterone level of less than 11 nmol per liter and a free testosterone level of less than 220 pmol per liter. The clinical importance of an age-related reduction in the testosterone level 1 – 3 remains controversial. 4 , 5 Because of the uncertainty regarding the nature of testosterone deficiency in aging men, 6 – 9 recent guidelines have suggested that so-called late-onset hypogonadism be regarded as a clinical and biochemical state with advancing age, characterized by particular symptoms and a low level of serum testosterone. 10 , 11 However, few data on hypogonadism in aging men are available 4 , 8 , 12 because of the lack of evidence regarding the exact criteria for identifying testosterone deficiency in older men who do not have pathological hypogonadism. 6 , 13 Although a familiar array . . .