Childhood obesity is one of the most serious public health problems. The prevalence of obesity among children is increasing and may negatively affect their immediate health, but it can also lead to obesity in adulthood. The aim of the study was to compare BMI cut-off points by examining three main international references: the World Health Organization (WHO), the International Task Force Obesity (IOTF) and the US Center for Disease Control and Prevention (CDC). Ultimately, the study group consisted of 18,144 children and adolescents aged 6.5-17.5 years. Body mass was measured on medical scales with an accuracy of ± 100 g and height measurement was taken using a height meter with an accuracy of ± 0.1 cm three times. Underweight, overweight and obesity were calculated according to WHO, IOTF and CDC BMI international references. There were differences in the incidence of underweight between the classifications: 16.8% according to IATF, 5.3% according to WHO and 9.9% according to CDC. There were also differences in the incidence of overweight and obesity between the classifications: 13% according to IOTF, 19.7% according to WHO and 14.1% according to CDC. In the CDC and WHO studies, a significantly higher prevalence of childhood obesity (4.0% and 4.7%, respectively) was observed compared with IOTF (2.1%). The prevalence of overweight and obesity in this study was higher among boys compared to girls. However, estimates of prevalence of overweight and obesity differ in methods and reference cut-off points. Higher prevalence was obtained in IOTF classification, followed by the WHO and CDC classification.