This longitudinal study identified common summer care arrangements for adolescents and examined whether those arrangements predicted risk for obesity (Body Mass Index (BMI) [greater than or equal to] 85th percentile for age and gender) the following school year. Participants were a nationally representative sample of 1766 adolescents ages 10-18 from the Panel Study of Income Dynamics-Child Development Supplement. Results showed that, beyond measures of BMI taken before the summer and several demographic aspects known to predict obesity, youth whose summer arrangements involved regular participation in organized activities (e.g., sports) showed significantly lower risk for obesity than other youth. This was most evident during early adolescence. Youth whose regular summer arrangement was predominated by parent care without organized activity participation showed the greatest risk for obesity. (Contains 1 figure and 3 tables.)