To examine the association between sedentary leisure-time and all-cause mortality and differences in survival time. Prospective cohort study. Information on sedentary leisure-time, defined as TV viewing and/or sitting reading, was collected from 72003 Swedish adults who were 45-83 (median 60) years of age and completed a self-administered questionnaire at baseline and were followed up for 17years through linkage with the Swedish Death Register. The association between sedentary leisure-time and all-cause mortality was modified by age with a more pronounced association in middle-aged (<60years of age) than in older adults (≥60years of age) (p-interaction<0.001). During follow-up, 3358 and 15217 deaths occurred in the middle-aged and older age group, respectively. The multivariable-adjusted hazard ratios for the highest (>6h/day) versus lowest category (<1h/day) of sedentary leisure-time were 1.72 (95% confidence interval [CI] 1.29-2.30) in middle-aged adults and 1.19 (95% CI 1.05-1.36) in older adults. This corresponded to a difference in survival time of respectively 2.4 (95% CI -4.1 to -0.8) years and 1.5 (95% CI -2.2 to -0.7) years. Prolonged sedentary leisure-time was associated with a significantly decreased survival time up to 2.4 years in middle-aged adults.