This study sought to determine cumulative lifetime exposure to environmental tobacco smoke (ETS) among urban women in relation to sociodemographic factors. In a population survey carried out in Geneva, Switzerland, during 1993-1995, a representative sample of 1, 883 women aged 35-74 years answered interview questions on lifetime ETS exposure. Exposed women were defined as those who had spent at least 1 hour daily in a smoky environment during 1 or more years. The prevalence of current ETS exposure was 31.0% among 1, 458 never or former smokers. Lifetime prevalence was 58.3% among 1, 061 never smokers. The home (42.1%) and the workplace (39.6% of employed women) were the most frequent sources of ETS exposure, leisure time activity being a secondary source. Throughout a lifetime, work accounted for the greatest average intensity of exposure (on average, 19 hours of exposure per week), while the longest duration of exposure (on average, 18 years) was in the home. Cumulative lifetime exposure (intensity (in hours/week) x duration) from all sources combined was 308 hours/week-years, which can correspond to 30.8 hours/week over a period of 10 years or 20.5 hours/week over a period of 15 years. Women from low socioeconomic classes had more intense and longer exposures than women from higher socioeconomic classes, mainly because of work exposure. Both the intensity and the duration of lifetime ETS exposure were greater than previously suspected. Reduction of ETS exposure in the workplace should be a public health priority. Am J Epidemiol 1998; 148: 1040-
