The purpose of this prospective study was to evaluate the sexual function of patients with benign prostatic hyperplasia (BPH) before and after transurethral resection of the prostate (TURP). The sexual functions of 155 patients with BPH were evaluated before TURP and 6 and 12 months afterwards. The mean age of the patients was 69 years (range 49-86 years). The only significant change in sexual function after TURP was improvement in early morning erections (P < 0.01). Sixty-eight per cent of the patients were satisfied with their sex life before TURP, 69% after 6 months and 67% after 12 months. The corresponding percentages of patients satisfied with their libido were 60%, 59% and 54%. Only 26% of the patients had completely satisfactory erections before TURP, while 22% had them 6 months later and 24% 12 months later. The proportion of fully impotent patients was 11% before the procedure, 13% after 6 months and 16% after 12 months. In 84% of the patients ejaculation was retrograde 6 months and 12 months after TURP. We conclude that TURP does not affect the sexual function of patients with BPH, with the exception of retrograde ejaculation.