Primary tumors of the diaphragm are very rare, From a clinical point of view, they do not present a specific symptomatology and the radiologic aspect is not characteristic. Their etiology is often obscure. The authors experienced one case of primary neurofibroma of the diaphragm. The patient was 52 year old male, and detected preoperatively abnormal round mass shadow in the middome portion of the left diaphragm in routine chest X-ray. A left posterolateral thoracotomy through the 7th ICS was performed. The mass and surrounding tissues were completely removed, and diagnosed as a primary neurofibroma by the histopathologic findings. Postoperative course was uneventful.