Sildenafil utilization was prospectively evaluated among 153 men with a history of erectile dysfunction (ED)-prescription drug use prior to starting sildenafil and 164 men who were new starters of ED-prescription drugs. Further, some determinants of sildenafil discontinuation were identified. During a median follow-up period of 18 months 45% of all patients discontinued sildenafil treatment, regardless of earlier treatment history. However, patients with a history of drug treatment for ED were nearly eight times as likely to switch or re-start another ED-prescription drug after discontinuing sildenafil compared to previously untreated users. Age >60 y, diabetes medication, nitrate use, and use of incontinence pads (a proxy for disease/surgery in the pelvic region) were associated with an increased likelihood of discontinuing sildenafil. Although the introduction of sildenafil reduced the barrier to seek medical help for erectile problems, sildenafil treatment failure in previously untreated patients results in a high dropout rate from further ED drug treatment of any kind.