The association between changes in body mass index over 1 year and measures of psychological functioning was evaluated in 314 boys and 253 girls with a mean age of 9 years. Anthropometric evaluations and standardized surveys were administered to students in all four-grade classes of seven suburban schools in the fall of two consecutive school years. Increases in body mass index were significantly associated with unfavorable changes in physical activity attitudes, activity preferences, perceived physical activity competence, self-concept, and body image. There was limited support for a hypothesis that overweight children are more sensitive to changes in body shape than non-overweight children. The finding of negative psychological consequences associated with increases in body mass index among children suggests that children may be overconcerned with body weight and shape.