Back lumbar hernia is a rare abdominal wall defect that usually presents spontaneously after trauma or lumbar surgery or, less frequently, during infancy (congenital). Few reports have been published in the literature describing primary lumbar hernia. A general surgeon will have the opportunity to repair only one or a few lumbar hernia cases in his/her lifetime. We report a case of a healthy 50-year-old man, with no previous surgeries or history of trauma, who presented to the outpatient department with abdominal discomfort, pain, and a sensation of a growing mass on his lower left back for 4 years. CT scan of the abdomen showed a mass in the left posterolateral abdominal wall. Specifically, a herniation of retroperitoneal fat between the erector spinae muscle group and internal oblique muscles through aponeurosis of the transversalis muscle (Grynfeltt hernia). The patient underwent a small lumbotomy, polypropylene mesh was placed and he recovered well. Although many techniques have been described for the surgical management of such hernias, none of them can be recommended as the preferred method. Our impression, however, is that the open approach, with a small lumbotomy, seems to be easy, safe and presents good postoperative recovery.