A long-term retrospective study was carried out on 790 cases of lung cancer to determine if the clinicopathologic characteristics and survival rates of lung cancer patients under the age of 50 differ from those of patients 50 years of age or older at diagnosis by analyzing data on patients registered at Tochigi Cancer Center Hospital. Of the 790 patients, 77 (9.7%) were under the age of 50 at diagnosis. The percentage of women in the younger patient group was significantly higher than that in the older patient group (39.0% vs. 27.5%; P = 0.034). Tumor histology revealed a significant preponderance of adenocarcinomas (60 patients, 77.9%) and a paucity of squamous cell carcinomas (8 patients, 10.4%) in the younger age group (P<0.001). The preponderance of adenocarcinoma was significant in both males and females (male: P = 0.004, female: P = 0.004). Smoking rates and rate of detection by cancer screening did not differ between the two age groups. Because of the paucity of smokers among the younger female patients, causes of lung cancer other than smoking should be sought in younger patients. No difference was found in the stage of the disease at presentation, treatment methods and survival rates between the two age groups. It is suggested that the prognosis for patients with lung cancer under the age of 50 is not significantly worse than for those aged 50 years or older, as has been shown by several investigators.