Background: Evidence is accumulating that sedentary behaviors have detrimental health effects. Comprehensive data on population changes in various sedentary behaviors over time are scarce. Purpose: This study aimed to determine changes in non-occupational sedentary behaviors in the Dutch adult population between 1975 and 2005. Methods: The National Time Use Survey of the Netherlands was used, which has been collected in 5-year intervals since 1975 (seven time points, n range=1017-2845). Adult participants completed a 7-day time-use diary in which they recorded their primary activity in 15-minute intervals throughout or at the end of the day. A validated method was used to determine time spent in various nonoccupational sedentary behaviors. Population-weighted analyses determining changes over time in various sedentary behaviors were carried out in 2011 and 2012. Results: Between 1975 and 2005, the proportion of non-occupational time spent sedentary remained relatively constant at ~60%. However, absolute time decreased, because of a 4.7-hour/week increase in occupational time. Sedentary occupational time could not be studied but has likely increased over these 3 decades. Most non-occupational sedentary behavior was during leisure, and the proportion of sedentary leisure time that comes from screen time increased from 26% in 1975 to 43% in 2005. Between 1975 and 2005, sedentary transport increased by 2 hours/week. Conclusions: The nature and distribution of sedentary behaviors in the Dutch adult population changed substantially over 3 decades. Screen-based activities are playing an increasingly dominant role.