Purpose We report the dropout rate associated with intracavernosal self-injection for erectile dysfunction at long-term followup, and determine parameters related to dropout. Materials and Methods Of 2,252 impotent patients evaluated during 9 years 450 (20%) enrolled in our self-injection program. Papaverine and phentolamine were given in 53% (initial treatment), prostaglandin E1 in 21%, and papaverine, phentolamine and prostaglandin E1 (triple mixture) in 26% of cases. Average injection volume for the 3 injection types was 0.52 cc. Data were retrospectively reviewed for patient dropout versus nondropout, specifically for type of drug, volume injected, changing treatment (from 1 drug and/or dosage to another), patient age, marital status, ethnic group, impotence duration and diabetes. Results Patient age ranged from 23 to 79 years (mean age 55). Of the patients treated at least 4 months 155 (35%) dropped out of the study. Mean treatment duration was 3.5 years. Logistic regression suggested that type of drug, changing treatment during the course of therapy and dosage (volume injected) were the only significant (p <0.05) parameters influencing dropout. Papaverine and phentolamine were twice as likely to lead to dropout as triple mixture or prostaglandin E1, and injection greater than 0.5 cc was more than twice as likely to lead to dropout. Demographic, ethnic, age and etiological factors had no significant effect on the overall dropout rate. Conclusions The effectiveness of injection therapy was an underlying factor determining the long-term dropout rate for patients with erectile dysfunction. Other parameters or combinations of parameters that may influence patient dropout remain to be explored.