Although certain risk factors are known to be associated with erectile dysfunction (ED), the demographic and ED characteristics of the population of men with ED are quite diverse. We examined results from randomized trials of sildenafil citrate (Viagra) to ascertain if efficacy differed across various subgroups of men with ED. In addition, we reviewed findings from long-term extension studies and published accounts of sildenafil use in clinical practice to determine if effectiveness is maintained with long-term sildenafil treatment and to determine if effectiveness in the clinic practice setting is consistent with that reported in clinical trials. Data were pooled from 11 double-blind, placebo-controlled, flexible-dose (taken as needed) studies to assess efficacy (N = 2667) of sildenafil in men (aged 23 to 89 years) with ED of broad-spectrum etiology who were not receiving concomitant nitrate therapy. Efficacy evaluations included the International Index of Erectile Function, a global efficacy question (“Did treatment improve your erections?”), and a patient-recorded event log of sexual activity. Significantly improved erectile function was demonstrated for sildenafil compared with placebo for all efficacy parameters analyzed (P <0.02 to 0.0001), regardless of patient age, race, body mass index, ED etiology, ED severity, ED duration, or the presence of various comorbidities. Long-term effectiveness was assessed in 3 open-label extension studies. Of those who continued long-term therapy (1 to 3 years) with sildenafil, >95% of patients reported that they were satisfied with the effect of treatment on their erections, and that treatment had improved their ability to engage in sexual activity. Findings from published accounts of sildenafil use in the clinical practice setting further demonstrated that sildenafil is an effective treatment for a wide range of patients with ED.