Few studies have addressed the association between television viewing time in childhood and overweight/obesity across the life course. Among 30,921 mother-daughter dyads from the Nurses' Mothers' Cohort (2001) and the Nurses' Health Study II (1989 and 1991), the following information was collected: daughter's television viewing time and physical activity (PA) level at ages 3-5 and 5-10 years, somatotype at ages 5 and 10 years, and body mass index at age 18 years and in adulthood (ages 26-45 years). According to multivariable-adjusted logistic regression models, television viewing at least 4 hours/day versus no television at ages 3-5 years was associated with odds ratios of overweight/obesity of 1.61 (95% confidence interval (CI): 1.20, 2.17) at age 5 years, 1.46 (95% CI: 1.14, 1.86) at age 10 years, 1.31 (95% CI: 1.00, 1.70) at age 18 years, and 1.32 (95% CI: 1.10, 1.59) in adulthood. A composite variable of high television viewing time/low PA level versus low television viewing time/high PA level at ages 3-5 years was associated with odds ratios of overweight/obesity ranging from 3.22 (95% CI: 2.23, 4.65) at age 5 years to 1.82 (95% CI: 1.36, 2.45) in adulthood. Findings were similar at ages 5-10 years. Long hours of television viewing in childhood alone and in combination with low PA levels were consistently associated with overweight/obesity throughout life.