Background: Physical activity (PA) may play a role in preserving kidney health. The purpose of this study was to determine if PA and sedentary behavior are associated with incident chronic kidney disease (CKD) and change in kidney function in older adults. Methods: The Health, Aging, and Body Composition study is a prospective cohort of 3075 well-functioning older adults. PA and television watching was measured by self-report, and serum cystatin C was used to estimate glomerular filtration rate (eGFR). CKD was defined as an eGFR3ml/min/1.73m(2). Discrete survival analysis was used to determine if baseline PA and television watching were related to 10-year cumulative incidence of CKD and rapid decline in kidney function. Results: Individuals who reported watching television >3 hours/day had a higher risk of incident CKD (HR 1.34; 95% CI, 1.09-1.65) and experiencing a rapid decline in kidney function (HR 1.26; 95% CI, 1.05-1.52) compared with individuals who watched television <2 hours/day. PA was not related to either outcome. Conclusions: High levels of television watching are associated with declining kidney function; the mechanisms that underlie this association need further study.