By studying a national population of children aged 10-17, we find that neighborhood parks/playgrounds have significant effects on childhood obesity (see below). Compared to girls without parks/playgrounds in their neighborhood, girls living in a neighborhood with a park or playground had lower BMI (by 2%). They were also 17% less likely to be obese and 28% less likely to be overweight. Similar, although smaller, park/playground effects were observed among boys. Boys living in neighborhoods with such facilities had slightly lower (1%) BMI and were 9% and 23% less likely to be obese or overweight.