The abdominal wall congenital lumbar hernia is a rare condition, There are around 50 cases describe in the English literature. These are classified according to their anatomical site of appearance, upper or lower lumbar triangle. Case presentation: A 6-year-old male patient presented congenital left mass in the lumbar region, reductible, size 10 x 8 cm; during abdominal ultrasound, hernia was compatible with Petits congenital hernia. A reduction of the hernial sack with anterior plasty and placement of the prosthetic mesh at the defect site was performed. Discussion: The triangle of Grynfelt-Lesshaft, is larger and more constant than the triangle of Petit, the latter represents the least common location. Several repair techniques are described, but anterior hernioplasty is the most recommended. Conclusion: Lumbar hernia should be considered as a differential diagnosis in all newborns with protruding mass on the left or right flank at birth, accompanied or not by another obvious or non-evident malformation. Early diagnosis avoids possible complications and allows for opportune treatment, allowing the patient a better lifestyle.