A study was made of histologic type of lung cancer in relation to smoking habit, year of diagnosis, age and sites of metastasis. It comprised 662 autopsies of men during the period from 1955 to 1972. As classified by the WHO system, 35.2 percent were epidermoid carcinoma, 24.6 percent were small cell carcinoma, 25.2 percent were adenocarcinoma and 14.2 percent were large cell undifferentiated carcinoma. The six non-smokers of the series were all found to be in class 3, adenocarcinoma. No clearcut and consistent relationships were observed. Although there was a steady decrease in the incidence of small cell carcinoma during this time period, this observation did not prove to be statistically significant. Small cell carcinomas increased with amount of smoking but not for all age groups. Adenocarcinomas decreased with advancing age but not in all smoking groups. Metastases were found in 96.3 percent of the cases and the sites most frequently involved were regional lymph nodes, liver, brain, distant lymph nodes, adrenals and bone. Small cell carcinomas showed the greatest percentage of involvement for those major sites and for the same sites, epidermoid carcinoma showed the lowest percentage.