Our objective was to assess the effects of customized instructions and dose optimization on treatment satisfaction and improvement in erectile function (EF) with sildenafil citrate in men with erectile dysfunction (ED) who had not been previously treated with a phosphodiesterase-5 inhibitor. This 8-week, multicenter, open-label, flexible-dose (25, 50, or 100 mg sildenafil) study included 2 phases. During phase 1, patients took 50 mg sildenafil and followed the sildenafil sample package instructions. In phase 2, sildenafil dose could be adjusted on the basis of efficacy and tolerability, and investigators provided additional customized instructions. The primary efficacy variable was the satisfaction rate (defined as patients responding “very” or “somewhat” satisfied to the Erectile Dysfunction Inventory of Treatment Satisfaction [EDITS] Question 1). Other efficacy assessments included the International Index of Erectile Function (IIEF) and the percentage of successful sexual intercourse attempts. Of 1109 men (mean age, 54±13 years) treated, 867 completed the study. In phase 1, 75% of patients were very or somewhat satisfied with treatment. Mean EF domain score on the IIEF increased from 14.3 at baseline to 23.5, and 79% of sexual intercourse attempts were successful. In phase 2, 53% of patients increased their sildenafil dose to 100 mg and 2% decreased to 25 mg. Satisfaction with sildenafil increased to 86%, 91% of sexual intercourse attempts were successful, and mean IIEF EF domain score increased to 25.7. Of the 196 men who were not initially satisfied at the end of phase 1, 64% became very or somewhat satisfied with treatment by the end of phase 2. Initially high levels of efficacy and satisfaction with sildenafil were achieved when patients were provided with only the sample package instructions and the recommended 50-mg starting dose. These results were enhanced with dose optimization, individual patient counseling, and customized instructions.