Extracorporeal shockwave therapy (ESWT) has been reported to improve the symptoms of Peyronie's disease. However, the response rates to this treatment appear to be variable. This study aimed to determine whether any patient or plaque characteristics are associated with a better outcome.A series of 36 patients with Peyronie's disease received ESWT as a primary treatment. Subjective response rates were compared on the basis of patient age, degree of pretreatment penile curvature, predisposing medical factors, duration of disease, and extent of plaque calcification.Ten men (27.8%) reported subjective improvements in curvature after ESWT. Of the factors considered, only age and pretreatment curvature influenced outcomes: 50% of the men below the mean age reported improvement compared with 5.6% of older men and 62.5% of men with mild curvature reported improvement compared with 8.3% of those with severe curvature.The response to EWST is not the same for all men with Peyronie's disease. Younger men and those with milder curvature have the best outcomes.