Carcinosarcoma accounted for 0.27% of nearly 3000 lung cancers examined in this department. All the patients were men aged between 44 and 62 years, and a majority of the tumours occurred in the left lung. Three patients died within six months of lung resection and in each case a postmortem examination was performed. In seven the carcinomatous component was a squamous-celled growth, and in one columnar-celled; the histology of the sarcomatous element varied. Carcinosarcomas form a distinct group of malignant lung tumours. In five cases sarcomatous transformation of the stroma had occurred and was considered to be the usual means by which the mixed type of growth arises. The other three were considered to be "collision" tumours. Carcinomatous metastases without sarcomatous change were seen in lymph nodes in three cases, and in three fatal cases sarcomatous tumour had recurred.