We investigated the effect of early sildenafil dose optimization and personalized instructions on sexual intercourse success in 1109 men beginning sildenafil therapy for erectile dysfunction. In phase 1 (4 weeks), patients followed the instructions contained in the sildenafil (50 mg) sample pack and had 1.4 sexual intercourse attempts per week with 82% success. Patients (17%) had a second intercourse attempt (80% successful): 58% occurred within 4 h, 20% within 5-8 h, and 22% within 9-24 h of the first attempt. In phase 2 (4 weeks), sildenafil was adjusted as needed (53% to 100 mg, and 2% to 25 mg), and investigators provided personalized instructions to facilitate patient success. Sexual intercourse attempts increased to 1.7 per week, with 91% success, and 18% were followed by a second attempt, of which 91% were successful. Most patients requested the 100-mg dose, which helped improve sexual intercourse frequency, flexibility and success.