• A patient whose symptoms had suggested the possibility of chronic appendicitis was found to have a chylothorax on the right side. Open thoracotomy revealed a tumor, cylindrical in form, involving the entire thoracic duct. The tumor was removed, with the duct contained in it, and the normal duct tissue at either end was ligated. Suggestions of interstitial edema in the upper abdominal area appeared after the operation but disappeared in about five days. In all other respects the patient did exceedingly well and is still well two years after the operation. The tumor was found to be a lymphangioma of the thoracic duct. This experience establishes the fact that the main thoracic duct can be ligated with impunity and that extensive portions of it can be excised without endangering the patient's life.