Introduction: The diagnosis of lumbar hernia can be easily missed, as it is a rare case to which most orthopedists are not exposed in their common clinical practice. Approximately 300 cases have been reported in the literature since it was first described by Barbette in 1672. Case Presentation: A 76-year-old woman who had been diagnosed with a femoral intertrochanteric fracture was sent to our department. Physical examination revealed a smooth, soft, and movable mass, with no tenderness, palpable on her left flank, which had gradually increased during the last seven years and presented with a slight feeling of swelling. We initially misdiagnosed the case as a left lipoma combined with the femoral intertrochanteric fracture. However, after six hours, the patient presented with a sudden onset of nausea, vomiting, and abdominal distension. Afterward, computed tomography (CT) examination confirmed that the mass was a spontaneous lumbar hernia. Conclusions: A lumbar hernia may, on rare occasions, become incarcerated or strangulated, with the consequent complication of mechanical bowel obstruction. We suggest that a patient with a flank mass should always raise suspicions of a lumbar hernia.