A series of 446 patients with lung cancer, comprising all cases diagnosed in a defined population of approximately 300,000 persons during a period of 4 yr, were studied prospectively and followed for 5 yr or until death. Histologic or cytologic confirmation of the diagnosis was achieved in 431 cases (97%). Only 140 patients (31%) were alive 1 yr after diagnosis, and only 19 patients (4%) were alive after 5 yr, with no significant difference between the men and women. The 5-yr. survival rates among patients with epidermoid. small-cell anaplastic, and adenocarcinoma were 6, 2, and 4%, respectively. The patients could also be divided into prognostically meaningful groups according to the symptomatic staging proposed by Feinstein. Of the 427 patients who had died within 5 yr, 410 (96%) had died of lung cancer and only 17 (4%) had died of other diseases.