OBJECTIVE: Unwarranted underestimation and overestimation of personal weight status may prevent weight maintenance behaviour. The present study reports on correlates of under- and overestimation of personal weight status and the association with weight maintenance intentions and self-reported action. DESIGN: Comparison of three cross-sectional surveys, representing different population groups. SUBJECTS: Survey 1: 1694 adolescents 13-19 years of age; survey 2: 979 nonobese adults 25-35 years of age; survey 3: 617 adults 21-62 years of age. MEASUREMENTS: Self-administered written questionnaires (surveys 1 and 3) and telephone-administered questionnaires (survey 2); self-reported BMI, self-rated weight status, intentions and self-reported actions to avoid weight gain or to lose weight, sex, age, education and ethnic background. Respondents were classified as people who are realistic about personal body weight status or people who under- and overestimate their body weight status, based on BMI and self-rated weight status. RESULTS: Most respondents in the three survey populations were realistic about their weight status. Overestimation of weight status was consistently more likely among women, whereas underestimation was more likely among men, older respondents and respondents from ethnic minorities. Self-rated weight status was a stronger correlate of intentions and self-report actions to avoid weight gain than weight status based on Body Mass Index. CONCLUSIONS: Relevant proportions of the study populations underestimated or overestimated their bodyweight status. Overestimation of personal weight status may lead to unwarranted weight maintenance actions, whereas underestimation may result in lack of motivation to avoid further weight gain.