We examined the association of adolescent obesity with participation in sports among 5489 low-income, inner city public high school students. Among inner city youth 28.5% of males and 33.7% of females were overweight and 15.9% of boys and 16.4% of girls were obese. For both males and females, participation in an increasing number of athletic activities was associated with lower (body mass index) BMI after controlling for age, grade, and playing football. While youth with lower BMI might be more likely to participate in sports, after school sports are a potential opportunity for prevention of obesity in adolescents.