Retroperitoneal lymphangioma is extremely rare. It may obstruct or invade surrounding vital organs, which may result in lethal effects to the host. Although surgical excision has been suggested as the first choice for treatment, complete extirpation is often impossible. Moreover, the rates of postoperative morbidity and disease recurrence remain high. We report a case of a huge retroperitoneal lymphangioma extending to the flank and scrotum that was successfully treated by intralesional OK-432 sclerotherapy without any serious complications.