Lymphangiohemangiomas of the mediastinum are exceedingly rare and few cases have been published in the English literature. This report may be the only reported case in which lymphangiohemangiomas were found bilaterally. We report a case of a 7-year-old boy with an incidental finding of an abnormal mediastinal shadow on a chest X-ray. The chest CT showed a large mass in the left superior mediastinum and another in the right posterior mediastinum. The left mass had anomalous venous channels connected to the left innominate vein, and the right mass to the left atrium. We performed an excision of the mass in the left side first and then the right side one month later. Anomalous venous channels were dissected carefully and ligated. There were no complications and no signs of recurrence 30 months after the operation.