Adenosquamous carcinoma is a rare, but pathologically distinct, form of lung cancer. Seven cases involving unequivocal squamous and glandular differentiation were studied. These cases accounted for 0.6 per cent of the 1,125 primary lung cancers examined at a metropolitan hospital during a 15-year period. The tumors measured from 1.3 to 5.5 cm in diameter. Five were peripheral, and two were associated with scars. Three of five resected specimens had regional lymph node metastases. Five patients had died of the disease within two years of diagnosis, and two were short-term survivors.