Aim: To study self-esteem in clinical sample of obese children and adolescents. Methods: Obese children and adolescents aged 8-19 years (n = 107, mean age 13.2 years, mean BMI 32.5 [range 22.3-50.6], mean BMI z-score 3.22 [range 2.19-4.79]; 50 boys and 57 girls) were referred for treatment of primary obesity. Self-esteem was measured with a validated psychological test with five subscales: physical characteristics, talents and skills, psychological well-being, relations with the family and relations with others. A linear mixed effect model used the factors gender and adolescence group, and the continuous covariates: BMI z-scores, and BMI for the parents as fixed effects and subjects as random effects. Results: Age and gender, but neither the child's BMI z-score nor the BMI of the parents were significant covariates. Self-esteem decreased (p < 0.01) with age on the global scale as well as on the subscales, and was below the normal level in higher ages in both genders. Girls had significantly lower self-esteem on the global scale (p = 0.04) and on the two subscales physical characteristics (p < 0.01) and psychological well-being (p < 0.01). Conclusion: Self-esteem is lower in girls and decreases with age. In treatment settings special attention should be paid to adolescent girls.