The effects of open prostatectomy, transurethral resection, transurethral vaporization, doxazosin and finasteride on sexual functions of men were investigated in a total of 305 patients with benign prostatic hyperplasia. The sexual functions of the patients were assessed with a questionnaire before treatment and 3 and 6 months after the treatment. A total of 212 (70%) patients were judged to be potent before the treatment. At 3 months, open prostatectomy and transurethral resection caused erectile dysfunction in 2 of 40 (5%) and 5 of 89 (6%) potent patients, respectively. At 6 months, one of the patients from the former and 2 of the patients from the latter groups who developed erectile dysfunction at 3 months stated improvement. Transurethral vaporization caused loss of erectile functions in 4 of 14 potent patients (29%) at the 3-month follow-up and, one of these patients recovered erectile functions at 6 months. Only one of the 33 patients (3%) using doxazosin stated that he lost his erectile functions both at 3 months and 6 months. At 3 months follow-up, finasteride caused loss of erectile functions in 8 of 36 potent patients (22%). Four of these patients underwent surgery (transurethral resection) after 3 months of finasteride use. At the 6-month follow-up, 3 more patients suffered from loss of erectile functions. We suggest that finasteride and transurethral vaporization have the greatest potential of impairing the sexual functions among the treatment options investigated in this study and that they must be carefully offered to the potent patients.