The data on short-term outcome of treatment for male erectile disorder demonstrate various success rates. Sporadic studies with psychological treatment modalities have reported success rates of up to 80%. Some studies (Masters and Johnson 1970) suggest fairly high failure rates - up to 40.6%. In contrast, the success rates of some biological treatment modalities are consistently quite high across various studies, with the highest success rates being reported for sildenafil (70%-80%), vacuum erectile devices (up to 90%), and penile prostheses (up to 95% in some studies). However, most of these studies are marred by numerous methodological deficiencies beyond the scope of this chapter. One may quite safely conclude that the short-term efficacy rates of treatments for male erectile disorder are fairly high. Presumably, a combination of biological and psychological treatment modalities could provide a still higher success rate. However, good studies on combined treatments - for instance, sildenafil and sexual counseling - have not yet been published.

Long-term treatment efficacy poses a bigger problem. The long-term efficacy rates of psychological treatment modalities are not well documented. Wide differences in relapse rates have been reported, ranging from 11% at a 5-year follow-up (Masters and Johnson 1970) to an almost complete absence of therapeutic gain of sex therapy at a 1-year follow-up (Levine and Agle 1978).

The long-term efficacy and satisfaction rates of biological treatment modalities also vary or are not available. Most patients stop using vacuum erectile devices after several months (Mobley and Baum 1998). As noted, a high discontinuation rate is seen at 6-month follow-up for the alprostadil suppositories. Intracavernous injection of alprostadil serves only as a palliative therapy for the majority of patients with erectile dysfunction (Sexton et al. 1998), and about half of patients (46.4% in one study [Kunelius and Lukkarinen 1999]) discontinue treatment with intracorporeal prostaglandin E1. Good data on the long-term use of the new oral preparations - sildenafil, phentolamine, and apomorphine - are still lacking. Penile prostheses usually have a fairly high long-term efficacy and satisfaction rate. We definitely need more long-term outcome studies, both for individual treatment modalities of erectile dysfunction and for the combination of biological and psychological treatment modalities. Prognostic studies, focused on predictors of treatment outcome, are also needed; these studies would help us to match patients to the most suitable, efficacious, and satisfactory treatment modality.