PURPOSE: To examine the associations among physical activity (PA), sedentary time (SED), and TV viewing (TV) with fat mass (FAT) and visceral adipose tissue mass (VAT) from childhood through adolescence (5-19 years). METHODS: Participants in the Iowa Bone Development Study (n = 230 males and 233 females) were examined at ages 5, 8, 11, 13, 15, 17 & 19 years. Accelerometers measured moderate- or vigorous-intensity PA (MVPA; min/day), light-intensity PA (LPA; min/day), and SED (h/day). Parent-proxy report (5 & 8 years) and child-report (11, 13, 15, 17, & 19 years) measured TV (h/day). DXA scans measured FAT (kg) and VAT (g). Sex-specific growth models were used to create FAT and VAT growth curves for individual participants (level 1), and to test the effect of MVPA, LPA, SED, & TV (level 2) after adjusting for weight, height, linear age, non-linear age, and maturity. RESULTS: Growth models indicated that low levels of MVPA were associated with high levels of FAT and VAT for males and high levels of FAT for females. TV was positively associated with FAT and VAT for males and females. LPA was positively associated with FAT in males. SED was not associated with FAT or VAT for males or females (p > 0.05). CONCLUSION: This study supports current PA guidelines focusing on MVPA rather than SED. The contribution of high TV, but not high SED, to high levels of adiposity suggests that TV's contribution to obesity is not just a function of low energy expenditure.