There is considerable evidence for an association between obesity and impaired executive function (EF) in adolescents and adults. However, little research has examined EF in overweight or obese children. Furthermore, data on EF in underweight individuals is lacking. In addition, there is no consensus on the directionality of the relationship between Body Mass Index (BMI) and EF, and longitudinal studies are rare. Thus, the present study examined whether children differ in their performance on a battery of EF tasks depending on their weight status (underweight, normal-weight, overweight), and investigated the longitudinal cross-lagged associations between EF and BMI. Hot EF (delay of gratification, affective decision-making), cool EF (attention shifting, inhibition, working memory [WM] updating), and BMI were assessed in 1,657 German elementary-school children at two time points, approximately oneyear apart. Overweight children exhibited slightly poorer attention shifting, WM updating, and affective decision-making abilities as compared to normal-weight children. Unexpectedly, they did not show any deficits in inhibition or delay of gratification. EF levels of underweight children did not differ significantly from those of normal-weight children. Furthermore, poor attention shifting and enhanced affective decision-making predicted a slightly higher BMI oneyear later, and a higher BMI also predicted poorer attention shifting and WM updating oneyear later. The latter association between BMI and subsequent EF scores, however, diminished when controlling for socioeconomic status. Results indicate that hot and cool EF plays a role in the weight development of children, and might be a promising factor to address in preventive interventions.