Abbreviations & Acronyms ED = erectile dysfunction EHS = erection hardness score LI-SWT = low-intensity shock wave therapy MPCC = mean penile circumferential change NO = nitric oxide PDE5i = phosphodiesterase type-5 inhibitor SHIM = sexual health inventory for men SRE = sleep-related erection VEGF = vascular endothelial growth factor Objectives: To evaluate the efficacy of low-intensity shock wave therapy and to identify the predictive factors of its efficacy in Japanese patients with erectile dysfunction. Methods: The present study included 57 patients with erectile dysfunction who satisfied all the following conditions: more than 6-months history of erectile dysfunction, sexual health inventory for men score of ≤12 without phosphodiesterase type-5 inhibitor, erection hardness score grade 1 or 2, mean penile circumferential change by erectometer assessing sleep related erection of <25 mm and non-neurological pathology. Patients were treated by a low-energy shock waves generator (ED1000; Medispec, Gaithersburg, MD, USA). A total of 12 shock wave treatments were applied. Sexual health inventory for men score, erection hardness score with or without phosphodiesterase type-5 inhibitor, and mean penile circumferential change were assessed at baseline, 1, 3 and 6 months after the termination of low-intensity shock wave therapy. Results: Of 57 patients who were assigned for the low-intensity shock wave therapy trial, 56 patients were analyzed. Patients had a median age of 64 years. The sexual health inventory for men and erection hardness score (with and without phosphodiesterase type-5 inhibitor) were significantly increased (P < 0.001) at each timepoint. The mean penile circumferential change was also increased from 13.1 to 20.2 mm after low-intensity shock wave therapy (P < 0.001). In the multivariate analysis, age and the number of concomitant comorbidities were statistically significant predictors for the efficacy. Conclusions: Low-intensity shock wave therapy seems to be an effective physical therapy for erectile dysfunction. Age and comorbidities are negative predictive factors of therapeutic response.