Environmental tobacco smoke (ETS) is among the most common environmental health risks, with a striking and immediate biological response and increased disease risk. Exposure studies have looked mostly at worksite or home exposures, whereas total exposure levels at the population level are rarely reported. This study examined ETS exposure at work, at home, and during leisure time in a cross-sectional population sample of working-age adults. Our aim was to monitor changes in ETS exposure from 1992 to 2002. More detailed information on duration of exposure, distribution of exposure sites, and patterns of exposure was obtained in 2002. Data were based on Finland's national population chronic disease risk-factor surveys (conducted every 5 years). Total sample size varied from 8,000 to 13,500. The survey includes a self-administered questionnaire about ETS exposure at different sites. The proportion of nonsmoking persons exposed to ETS declined throughout the study period among both men and women. In 2002, 5.9% of male and 3.6% of female nonsmokers were exposed to ETS 1 hour or more per day, whereas 5.8% of men and 1.7% women were exposed less than 1 hour daily. Worksite exposure was more common among younger age groups of both sexes, but nonsmoking women in older age groups received more exposure at home than at worksites. Policy developments on ETS should aim to protect the whole population from ETS in all environments given that health risks from ETS often persist at home and in leisure environments. Total exposure levels should be studied to assess the health impacts of ETS.