In tabulating the smoking habits of 95,744 residents of the San Francisco Bay Area, as reported between July 1979 and June 1984 at multiphasic health checkups, the prevalence of current smoking was found to be higher in men than in women aged 30 years and above, but in those younger than 30 the reverse was true. In every age group, compared with male smokers, female smokers tended to smoke fewer cigarettes per day, to inhale less and to smoke cigarettes with lower tar and nicotine yield. Blacks showed the highest percentage of smokers, whites were second highest and Asians were lowest, with Asian women being substantially lower than other race-sex groups. On average, white smokers smoked more cigarettes per day and inhaled more than did black smokers, but whites were more apt to smoke low-yield cigarettes. Compared with a 1964 to 1968 study in the same setting, there has been a decrease in the prevalence of cigarette smokers but, among smokers, a higher proportion in 1979 to 1984 smoked at least 20 cigarettes per day. During the 1979 to 1984 period, there were small downward trends in the prevalence of cigarette smoking in men and white women and in the prevalence of heavy smoking among male smokers, but there was no apparent increase in the use of lower-yield cigarettes by smokers. Although this study group contained relatively fewer smokers, most of the age, sex and racial differences and long-term trends parallel what has been observed nationally.