Lung cancer in patients younger than 40 years of age. The records of 52 patients younger than 40 years of age who had bronchogenic carcinoma diagnosed between 1965 and 1985 were reviewed. The preponderance of adenocarcinoma (54%), the lower male-female ratio in this age group compared with patients age 40 or older (2:1), the importance of cigarette smoking as a causative factor (80% of patients), the long mean duration of symptoms (5 months), and the high incidence of advanced stage at diagnosis (77% Stages III and IV) in these patients are findings similar to those reported in other published series. There was no significant difference in resectability (23% versus 19%), median survival length (5.3 months versus 6.9 months), median survival length of patients who had surgical resection (10.5 months versus 10.8 months), and 5-year survival rate (11.5% versus 6.3%) in these patients compared with a randomly selected group of 260 patients with lung cancer who were age 40 or older. 