The incidence of lung cancer is increasing dramatically worldwide. Cancer of the lung, the number one cause of death from cancer in men in the United States, will soon surpass breast cancer to become the most frequent cause of cancer death in women. To detail the changing pattern of lung cancer, we reviewed the clinical features of all 1752 patients whose lung cancer was diagnosed at the Lahey Clinic from 1957 through 1980. Women comprised a constant proportion of the total number of clinic patients during this 24-year period. Lung cancer in women increased markedly from 13% of all patients (1 to 6.8 ratio of women to men) in 1957 through 1960 to 35% (1 to 1.8 ratio) in 1977 through 1980. The authors reviewed pathologic specimens of 394 women with lung cancer. No significant change occurred in cell type distribution over the years: adenocarcinoma, 38%; epidermoid carcinoma, 20%; large cell carcinoma, 15%; small cell undifferentiated tumor, 13%; and other cell types, 14%. The incidence of all lung cancer cell types (Kreyberg Group 1 and Group 2) increased in women who smoked. Our study suggests that smoking is a major causal factor in the rising occurrence of all lung cancer cell types in women as contrasted to the preponderance of Kreyberg Group 1 tumors in men who smoke.