We describe a case in whom recurrent pneumonia was the presenting manifestation of a benign cystic teratoma of the mediastinum. Although the symptoms had developed over a 15-year period, the mass was not identified on the chest roentgenograrns up to the age of 22 years. CT demonstrated the extent of the mass, but failed in clarifying the cystic nature of the tumor and in providing diagnosis. The lesion could be safely approached through an antero-lateral thoracotomy, saving major chest wall muscles. However, surgical removal of the mass was difficult because of firm adherence to surrounding structures.