OBJECTIVE-We investigated whether television (TV) viewing and low leisure-time physical activity in adolescence predict the metabolic syndrome in mid-adulthood. RESEARCH DESIGNANDMETHODS-TV viewing habits and participation in leisuretime physical activity at age 16 years were assessed by self-administered questionnaires in a population-based cohort in Northern Sweden. The presence of the metabolic syndrome at age 43 years was ascertained in 888 participants (82%of the baseline sample) using the International Diabetes Federation criteria. Odds ratios (ORs) and CIs were calculated using logistic regression. RESULTS-The overall prevalence of the metabolic syndrome at age 43 years was 26.9%. Adjusted OR for the metabolic syndrome at age 43 years was 2.14 (95% CI 1.24-3.71) for those who reported "watching several shows a day" versus "one show/week" or less and 2.31 (1.13-4.69) for leisure-time physical activity "several times/month" or less compared with "daily" leisure-time physical activity at age 16 years. TV viewing at age 16 years was associated with central obesity, low HDL cholesterol, and hypertension at age 43 years, whereas low leisure-time physical activity at age 16 years was associated with central obesity and triglycerides at age 43 years. CONCLUSIONS-Both TV viewing and low leisure-time physical activity in adolescence independently predicted the metabolic syndrome and several of the metabolic syndrome components in mid-adulthood. These findings suggest that reduced TV viewing in adolescence, in addition to regular physical activity, may contribute to cardiometabolic health later in life.