The article published in the March 26, 2012, issue of the Archives on the association between sitting time and all-cause mortality raises important public health questions. Van der Ploeg et al1 reported that prolonged sitting was a risk factor of all-cause mortality, independent of physical activity, body mass index, age, and sex. Indeed, the study of sedentary behavior (SB) has become a popular research niche, with reports now demonstrating an independent association with chronic disease and mortality.2- 4Sedentary behavior is not synonymous with extremely low physical activity levels because these factors each independently contribute to diabetogenic and atherogenic outcomes.4 Thus, it is plausible to have a potentiated risk profile if someone is both inactive and engages in extended bouts of SB. Although the study by van der Ploeg et al1 does not provide objective SB measures, the authors compiled survey data and mortality records from more than 220 000 adults and reports that during 621 695 follow-up person-years, mortality hazard ratios were 1.02, 1.15, and 1.4, for 4 to less than 8, 8 to less than 11, and 11 hours or more of sitting per day, respectively, compared with less than 4 hours per day. Importantly, the authors went further to demonstrate the impact of SB by estimating the population-attributable fraction, which revealed that sitting was responsible for approximately 7% of all deaths.