Trocar-site incisional hernias are potentially dangerous because of their susceptibility to become Richter hernias. The authors describe a morbidly obese patient in whom developed an unusual type of Richter hernia after a laparoscopic isolated Roux-en-Y gastric bypass at a 10-mm trocar site. Although the fascial closure of the trocar hernia site was intact, a hernia developed through the peritoneum into the preperitoneal space. For morbidly obese patients, the thick preperitoneum is a potential space that allows for the development of a Richter hernia, despite adequate fascial closure. It is recommended that all 10-mm and 12-mm trocar sites be closed, incorporating the peritoneum into the fascial closure to obliterate the preperitoneal space, to prevent this postoperative complication.