Constipation is a symptom not to be neglected, especially if the complaint is recent. We report a case where this symptom was the only clinical manifestation of a voluminous retroperitoneal tumor. The tumor was found to be a neurilemmoma of the fourth right lumbar roots, confirmed at pathological examination. Manifestations of extradural neurinomas generally result from compression of neighboring structures. The best preoperative diagnosis approach is magnetic resonance imaging but histology is required for confirmation. The close relations the tumor mass maintains with the unaffected nerve fibers makes resection difficult without postoperative functional consequences. Surgeons discuss the relevance of partial excision in order to preserve the nerve root in case of a benign slow-growing tumor. There does however appear to be a significant recovery of muscle strength even in case of total resection.