Lymphangiomas are rare benign tumors of the lymphatic system. They usually occur in the neck or axillary region, whereas the retroperitoneum is one of the least frequent sites. The treatment of choice is complete surgical excision. We report a case of a 56-year-old man who had a retroperitoneal cystic lymphangioma in combination with bladder cancer. After complete surgical excision of the retroperitoneal lymphangioma with transurethral resection of the bladder tumor followed by intravesical BCG immunotherapy, the patient remained free of recurrence at 1 year after treatment.