Inguinal hernias often occur after radical retropubic prostatectomy (RRP). We present a novel and simple technique for preventing inguinal hernias after RRP, which any surgeon can complete within a few minutes. Methods: A total of 230 Japanese prostate cancer patients underwent RRP between January 2007 and September 2011. From July 2009, 115 patients underwent inguinal hernia prevention procedures at the same time as RRP. In this procedure, we released approximately 5 cm of the bilateral vas deferens and spermatic vessels from the peritoneum. In cases in which the processus vaginalis had spread into the abdomen, we ligated it close to the peritoneal cavity and then transected it. The remaining 115 patients who underwent RRP but did not undergo the hernia prevention procedure were used as the control group. The incidence rate of postoperative inguinal hernia was compared between the 2 groups. Results: Inguinal hernias developed during the postoperative follow-up period in 18 of the 115 control patients (15.7%) (median duration, 50 months). The hernia-free survival rate of this group was 89.6% and 84.1% at 1 and 2 postoperative years, respectively. In contrast, only 1 of the 115 patients (0.87%) who underwent the hernia prevention procedure developed an inguinal hernia during the follow-up period (median duration, 27 months). The hernia-free survival rate of this group was 100% at both 1 and 2 postoperative years (P<0.0001). Conclusions: We developed a simple method for preventing post-RRP inguinal hernias. The procedure is easy to perform and produces excellent outcomes.