We examined the impact of school performance measured in terms of grade point averages (GPAs) in early and middle adolescence (ages 9, 12, and 15), and the impact of school performance throughout the different school stages on adult obesity. The participants were 732 healthy women and men derived from a population-based Cardiovascular Risk in Young Finns Study. GPAs were measured at the ages of 9, 12, and 15. The body mass index (BMI; kg/m(2)), and the waist circumference (WC) were conducted participants being aged 27 or 30. Birth weight, childhood BMI, adulthood physical activity, maternal and paternal BMI, and maternal education were controlled for. The results showed that low GPAs in each measurement and low GPAs throughout the comprehensive school were a risk factor of adulthood obesity, but only among women. The association remained when controlling for potential confounding variables (p-values in the fully adjusted models 0.026, 0.007, and 0.004 at the ages of 9, 12, and 15, respectively). The results were similar when the BMI was used as a dichotomous variable (BMI > or = 30 and BMI < 30). Low school performance has previously been associated with higher rates of smoking and alcohol consumption later in life. Our result underscores that low school performance is a health risk factor that should be taken seriously in preventive health education.