Carcinosarcoma is an uncommon pulmonary malignancy characterized by carcinomatous parenchyma and sarcomatous stroma. The cytologic, immunohistochemical and ultrastructural features of a case of pulmonary carcinosarcoma suspected by fine needle aspiration cytology is presented. Only bizarre spindle cells arranged in loose groups, in microtissue fragments and in a dissociate fashion were present in the aspiration smears. They were markedly positive for vimentin. The epithelial component was not found, which was probably due to marked paucity of carcinomatous component that was proved by histologic examination of the resected tumor. The diagnosis of pulmonary carcinosarcoma should be considered whenever poorly differentiated epithelial cell groups with a malignant mesenchymal component set in a myxoid background are seen in a pulmonary cytology specimen.