Durable techniques that prevent postoperative inguinal hernia (IH) after robot-assisted radical prostatectomy (RARP) have not been established. This study evaluated the long-term efficacy of a postoperative IH prevention technique that uses no artificial agents to assess the characteristics of IH occurrence after introducing this technique. We retrospectively analyzed 201 consecutive patients who underwent RARP at our institution between September 2011 and February 2014. In total, 189 cases were eligible for the study. The non-IH prevention and IH prevention groups comprised 72 and 117 cases, respectively. We compared the incidence of IH between the two groups using Kaplan-Meier curves. Risk factors for IH in the prevention group were determined via multivariable logistic regression analysis. The rate of IH occurrence was 20.8% (15 cases) in the nonprevention group and 8.5% (10 cases) in the prevention group, with median follow-up periods of 99.5 and 89.9 months, respectively. The Kaplan-Meier curves indicated a significant difference between the two groups (p = 0.011). Only cutting of the vas deferens significantly contributed to reduced occurrence of IH in multivariable analysis (p = 0.047). After reviewing the intraoperative videos, insufficient separation of the vas deferens was considered the main cause of IH in the prevention group. Our simple prevention technique with no artificial agents had a durable effect on IH prevention after RARP over a median follow-up period of more than 7 years. Cutting the vas deferens effectively prevented IH after RARP.