Prescription sales for testosterone products have substantially increased over the last several years reflecting the growing awareness of physicians for the potential benefits of testosterone replacement therapy in men with hypogonadism. Indiscriminate administration of testosterone poses a risk and has to be deprecated. Testosterone supplementation to treat late-onset hypogonadism (LOH), a term for androgen deficiency in elderly men, is still controversially discussed mainly due to a lack of large, controlled clinical trials on efficacy and safety. To provide guidance for physicians primarily dealing with aging men, ISSAM is periodically updating and publishing its recommendations as new data become available [Morales A, Lunenfeld B. International Society for the Study of the Aging Male. Investigation, treatment and monitoring of late-onset hypogonadism in males. Official recommendations of ISSAM. International Society for the Study of the Aging Male. Aging Male 2002;5:74-86 and Morales A, Lunenfeld B. Androgen replacement therapy in aging men with secondary hypogonadism. Draft recommendations for endorsement by ISSAM. Aging Male 2001;4:1]. Following a panel discussion at the 4th ISSAM Congress in Prague in February 2004, the International Society of Andrology (ISA), the International Society for the Study of the Aging Male (ISSAM) and the European Association of Urology (EAU) revised existing recommendations on the definition, diagnosis and management of LOH. The recommendations are based on the currently available scientific data on androgen supplementation therapy and should be regarded as provisional until larger-scale, long-term studies are available. While certainly not intending to be exhaustive, this review will highlight some relevant background information and provide the underlying scientific rationale for the ISA, ISSAM and EAU recommendations on LOH published in this issue.