Carcinosarcoma of the lung is a rare highly malignant tumor of unknown histogenesis. There is an epithelial carcinomatous component and a malignant mesenchmatous component with heterologous tissue. Survival at two years after surgical resection is not greater than 10%. We report a case observed in a 71-year-old man who developed chest pain. Outcome was fatal at three months. Pathology examination of a transparietal biopsy provided the diagnosis which was confirmed by immunohistochemistry on the surgical resection specimen.