RESUMEN
<p><b>OBJECTIVE</b>To evaluate the effects of tadalafil administered on demand or once a day in the treatment of erectile dysfunction (ED).</p><p><b>METHODS</b>We randomly assigned 61 ED patients to three groups to receive tadalafil on demand, at 5 mg once daily, and at 10 mg once daily, respectively. After 42 days of medication, we compared the therapeutic effects among different groups using the patients' sexual encounter profile (SEP) diaries, detected the adverse reactions and assessed the safety of tadalafil.</p><p><b>RESULTS</b>Fifty-three (86.7%) of the patients completed the investigation, and all responded well to tadalafil medication, with a significantly improved success rate of sexual intercourse and a low rate of mild adverse effects. The mean positive rates of SEP were basically similar between the on-demand and once-daily groups.</p><p><b>CONCLUSION</b>There are no significant differences in the improvement of penile erection and sexual satisfaction of ED patients treated by on-demand and once-daily administration of tadalafil.</p>