Background: Childhood obesity is one of the nation's foremost health challenges. How much of this is due to lifestyle choices? The objective of the study was to determine health behaviors that contribute to obesity in sixth-grade children. Methods: To assess which health habits contribute to childhood obesity, we studied body mass index, blood pressure, lipid profile, glucose, and heart rate recovery after a 3-minute step test among sixth-grade children enrolled in a school-based intervention study from 2004 to 2009, comparing health behaviors and physiologic markers in obese versus nonobese children. Univariate associations with obesity (P values ≤.10) were entered into a stepwise logistic regression to identify independent predictors. Results: Among 1,003 sixth graders (55% white, 15% African American; average age 11.5 years), 150 (15%) were obese. Obese students had higher levels of total cholesterol, low-density lipoprotein cholesterol, triglycerides, blood pressure, and recovery heart rates. They consumed more regular soda and school lunches but were less likely to engage in physical activities. Obese students were more likely to watch TV ≥2 hours per day. Independent predictors were watching TV or video games (odds ratio [OR] 1.19, 95% CI 1.06-1.33) and school lunch consumption (OR 1.29, 95% CI 1.02-1.64); moderate exercise was protective (OR 0.89, 95% CI 0.82-0.98). Conclusions: Obesity is present in 15% of our sixth graders and is associated with major differences in cardiovascular risk factors. Opportunities to improve childhood health should emphasize programs that increase physical activity, reduce recreational screen time, and improve nutritional value of school lunches. Whether genetic or not, childhood obesity can be attacked. © 2010 Mosby, Inc.