The main effect of testosterone was long-time assumed to be on sexual interest and, indirectly, on erectile function. Newer insights demonstrate that testosterone deficiency impairs the anatomical, ultrastructural, biological and physiological/functional substrate of penile erection, which can be, at least in part, restored by normalization of plasma testosterone levels. This is a report on a 56-year-old man suffering from diabetes mellitus type II and metabolic syndrome, who had complaints of a severe erectile dysfunction because of venous leakage, confirmed by pharmaco-cavernosography. He was also testosterone deficient (1.8 ng ml−1). Upon testosterone administration his erectile function improved dramatically. Repeated cavernosography no longer showed venous leakage.