We retrospectivelyevaluated postoperative inguinal hernias (PIHs) after robot-assisted radical prostatectomy(RARP) with a technique for preventing hernias byspermatic cord isolation. Among the RARPs performed from 2016 to 2018, 191 cases were evaluated 12 or more months after surgery. In all the cases, the peritoneum was isolated from the spermatic cord by5 cm or more as a hernia prevention technique during RARP. We compared the background factors between PIH-positive and PIH-negative groups. The PIH-positive group had a significantlylower bodymass index (BMI) than the PIH-negative group (20.6 kg/m2 vs 23.8 kg/m2, p＝0.0079), but there were no significant differences in other background factors. When patients were classified into three groups byBMI, low (＜21.9 kg/m2), intermediate (21.9 to 25.5 kg/m2), and high (＞25.5 kg/m2), the rate of PIH was 8.5% for the low group, 2.1% for the intermediate group, and 0% for the high group. Our findings suggest that incidences of inguinal hernias after the preventive technique of spermatic cord isolation in RARP, and the BMIs tended to be low in the hernia cases.