Lymphangiomas are relatively rare benign congenital tumors of the lymphatic system. They are usually discovered during childhood and typically occur in the neck and axillary regions. Retroperitoneal lymphangiomas are a rare occurrence and represent 1% of all cases. Here, we presented a 70-year-old male who presented with abdominal discomfort and chronic constipation in the last three years. A computerized tomography scan showed a giant abdominal hypodense cystic mass measuring 195 x 145 mm, which laminates the abdominal aorta, the left iliac vessels, and the left ureter. The patient underwent surgical exploration. Due to the giant cystic volume, it was carefully opened, aspirated, and removed. The histopathological examination showed a retroperitoneal lymphangioma. In conclusion, giant retroperitoneal lymphangioma in an adult is a rare occurrence. The primary treatment is complete surgical excision. Histopathological examination is essential for diagnosis confirmation.