Pulmonary carcinosarcoma(Sarcomatoid carcinoma of the lung) is a rare pulmonary malignancy, which is defined as having an admixtture of both carcinomatous and sarcomatous components. Pulmonary carcinosarcoma occurs most frequentlly in males between 50 and 80 years of age. It predominantly affects the upper lobe and/or the principal bronchi, and is associated with a history of smoking. Here, we report a case of pulmonary carcinosarcoma with a left lobe atelectasis due to an endobronchial mass in a 56-year-old male. After a left pneumonectomy, the pathologic stage was IIb (T3N0M0). Four months later, an abdominal mass was observed and exploratory laparotomy revealed metastases of the pulmonary carcinosarcoma to the pelvic cavity.