The distribution of cigarette smoking (as well as of cigar and pipe smoking in men) by occupation was examined in over 800,000 men and women age 45-70 who were enrolled in the American Cancer Society's prospective study in 1982. Striking variations were seen for men--less striking variations for women. Smoking rates were significantly higher in groups exposed to a number of occupational hazards, compared to groups not so exposed. A considerable amount of variation is related to social class, but some individual occupations exhibit notably high (law enforcement) or low (clergy) smoking rates. This information can be quite useful in planning morbidity or mortality studies of specific occupational groups or in analyzing data from existing studies.