BACKGROUND: There is lack of evidence-based optimization of the protocol for low-intensity shockwave therapy for erectile dysfunction. Furthermore, the safety and efficacy of repeating shockwave therapy have not been explored.AIM: To compare the efficacy and safety of 6 and 12 treatment sessions within a 6-week treatment period and investigate the effect of repeat treatment after a 6-month period in a 2-phase study.METHODS: Patients with vasculogenic erectile dysfunction that responded to phosphodiesterase type 5 inhibitors were randomized into 2 groups: low-intensity shockwave therapy sessions once (group A, n = 21) or twice (group B, n = 21) per week for 6 consecutive weeks (phase 1). Patients who completed 6-month follow-up were offered 6 additional sessions (phase 2); group A received 2 sessions per week and group B received 1 session per week. Patients were followed for 6 months.OUTCOMES: International Index for Erectile Function erectile function domain (IIEF-EF) score, minimally clinical important differences (MCIDs), Sexual Encounter Profile question 3 (SEP3) score, and triplex ultrasonographic parameters.RESULTS: In phase 1, groups A and B showed improvement in IIEF-EF score, MCID, SEP3 score, and mean peak systolic velocity compared with baseline. MCIDs were achieved in 62% of group A and 71% of group B, and the percentage of yes responses to SEP3 was 47% in group A and 65% in group B (P = .02). Mean peak systolic velocity at baseline and at 3-month follow-up were 29.5 and 33.4 cm/s for group A and 29.6 and 35.4 cm/s for group B (P = .06). In phase 2, group A showed a greater increase in the percentage of yes responses to SEP3 (group A = +14.9; group B = +0.3). When the impact of the total number of sessions received was examined, MCIDs in IIEF-EF score from baseline were achieved in 62%, 74%, and 83% of patients after 6, 12, and 18 sessions, respectively. No treatment-related side effects were reported.CLINICAL IMPLICATIONS: The total number of low-intensity shockwave therapy sessions affects the efficacy of erectile dysfunction treatment. Retreating patients after 6 months could further improve erectile function without side effects. 12 sessions can be delivered within 6 weeks without a 3-week break period.STRENGTHS AND LIMITATIONS: This study lacked a sham-controlled arm. However, all patients were randomized to different groups, and baseline characteristics were similar between groups. Also, all patients were confirmed by triplex ultrasonography to have arterial insufficiency.CONCLUSION: Patients can benefit more in sexual performance from 12 sessions twice per week compared with 6 sessions once a week. Shockwave therapy can be repeated up to a total of 18 sessions. Kalyvianakis D, Memmos E, Mykoniatis I, et al. Low-Intensity Shockwave Therapy for Erectile Dysfunction: A Randomized Clinical Trial Comparing 2 Treatment Protocols and the Impact of Repeating Treatment. J Sex Med 2018;15:334-345.