Plication of the hemidiaphragm is effective to relieve respiratory symptoms such as exertional dyspnea and orthopnea of the patients with unilateral diaphragmatic paralysis. We have experiences of 2 types of diaphragmatic plication;one for the symptomatic patients with unilateral diaphragmatic paralysis, and the other for the patients who underwent phrenicotomy during extended surgery for a recurrent thymoma. The former plication was performed for a therapeutic purpose to alleviate the patient's symptoms. The latter was performed for a prophylactic purpose to keep the patient free from possible symptoms or postoperative morbidity after phrenicotomy. Case 1:A 65-year-old female with an eventration of the right diaphragm underwent a sternal resection and reconstruction for a large desmoid tumor. After continuous mechanical ventilation for 3 months, she was still under noninvasive positive pressure ventilation( NPPV) for 24 hours a day. Plication of the right hemidiaphragm was performed and the patient was successfully weaned from NPPV. Case 2:A 41-year-old female with myasthenia gravis underwent a surgery for a recurrent thymoma. Left phrenicotomy was necessary to achieve a complete resection of the tumor. Plication of the left diaphragm was performed during the tumor resection to prevent possible respiratory complications. Postoperative course was uneventful, and her vital capacity was well maintained.