Lung cancer in patients under 40 years old is rare. Among 718 patients with lung cancer, 5% or 35 patients were younger than 40. All but one were heavy smokers. Twelve young patients who had operations survived 41.7 (SD 46.3) months: they included six who had resections of Stage 3 disease and who survived 19.2 (SD 16.0) months. The other six young patients treated operatively were free of nodal metastasis N0); all survived more than 3 years and three of them are apparently cured. The 23 young patients who were not treated operatively survived for 5.6 (SD 3.1) months. The 5 year survival rate of these young operated patients was not different from that of 201 operated patients over 40 years of age. Young nonoperated patients survived for a significantly shorter time (p less than 0.0001) than did the older patients who also received only chemotherapy and/or radiation as a treatment. In young patients adenocarcinomas predominated (48.6%), and the incidence of small cell undifferentiated cancers was high (28.6%). These significant differences as compared to the control group did not explain the short survival time of the young patients treated nonsurgically. We conclude that lung cancer in young persons is virulent and that diagnosis is frequently delayed. Therapy, in selected patients, should include aggressive resection, sometimes despite advanced local disease. This group of patients justifies innovative, intensive efforts at more prompt diagnosis and experimental multimodal therapy.