To measure the prevalence of physical inactivity, and variables associated with it, in an adult southern Brazilian population. Population-based cross-sectional study covering a multiple-stage sample of 3182 subjects aged 20 yr or more. Physical activity was assessed through the short version of the International Physical Activity Questionnaire (IPAQ), using home interviews with last-week recall. The questionnaire covers leisure, occupation, transportation, and housework activities. Physical inactivity was defined as fewer than 150 min.wk(-1) spent in moderate or vigorous physical activities. The time spent in vigorous activities was multiplied by two. The prevalence of physical inactivity was 41.1%. After multivariate analyses, inactivity was positively associated with age and socioeconomic status, and inversely associated with self-reported health status. Those with white skin color and women who live alone rather than with a partner were more likely to have physical inactivity. Body mass index showed a significant U-shaped relationship with inactivity among men. The prevalence of physical inactivity in this Brazilian adult population is high, even though lower than reported in studies of leisure-time activity alone in other populations. Studies in developing countries may be seriously biased if activities during labor, transportation, and housework are not assessed.