Retroperitoneal lymphangiomas are rare, benign cystic structures that are best evaluated with computed tomography and ultrasound. Preoperative diagnosis is often difficult, in part because there is little to distinguish them from other cystic masses and because the lesion is often not considered on the differential diagnosis. Surgery may be required as both a diagnostic and therapeutic measure. The cysts may be asymptomatic for years and then present because of compression of surrounding structures or pain. The treatment is as complete surgical excision as is possible. Bowel cleansing should be done preoperatively. The long-term results are excellent when total excision or near-total excision with marsupialization is accomplished.