Cytologic examination of sputum samples from an elderly patient revealed the presence of two cell populations: squamous cell carcinoma cells and rhabdomyosarcoma cells. The abnormal squamous cells showed both keratinizing and nonkeratinizing forms while some of the rhabdomyosarcoma cells showed cross striations. Sputum cytology was thus able to suggest a diagnosis of pulmonary carcinosarcoma. Histologically, the tumor was composed mainly of sarcomatous tissue showing various kinds of cells: fusiform or fibrous cells, round anaplastic cells, spindled cells with typical cross striations and myoblastic cells. A partially myxomatous degeneration was present. In addition, squamous cell carcinoma proliferated along the bronchi and formed small invasive cell nests in the sarcomatous tissue. No transition between the two components was noted. Both cellular constituents had metastasized to an interlobar lymph node.