Lumbar hernias are quite rare, even more so when primary or of spontaneous nature. These defects in the lumbar region demand a comprehensive knowledge of the anatomy of the lateral abdominal wall and paraspinal muscles. Given the proximity of bone structures, they can pose a surgical challenge when trying to achieve an ideal dissection and appropriate mesh overlap. The authors report the case of a primary Petit\'s hernia that underwent an open anterior surgical approach with the use of a preperitoneal mesh. In addition to the described surgical technique, the article also aims to detail the diagnosis and anatomic classification of this rare pathology.