Background: Both parents' and children's perception of children's weight status may be important predictors of slimming and energy-balance related behaviours, independent of children's actual weight status. Objectives: We examined the cross-sectional association of children's self-reported slimming and energy-balance related behaviours with children's (i) actual, (ii) self-perceived and (iii) parent-perceived weight status. Methods: Data of 10- to 12-year-old European children and their parents were used. Multilevel logistic and linear regression analyses were performed, adjusting for age, gender, parental weight controlling behaviours, education, marital status and ethnicity. Results: Independent of their actual weight status, a higher proportion of children reported slimming when they or their parents perceived them as too fat. Children's self-perceived weight status was more strongly associated with slimming than their parents' perception or their actual weight status. Moreover, children who perceive themselves as overweight reported less physical activity and more screen time. Children whose parents perceive them as overweight reported less physical activity. Conclusions: Children's own perception of their weight status appears to be more important for their self-reported slimming than their actual or their parent's perceptions of their weight status. Additionally, children's self-perceived weight status seems important in engaging more physical activity and reduces screen time.