246 Thailand, in the group of children aged 6–12 years, the incidence of overweight rose from 5.8% in 1997 to 6.7% in 2001 [1]. In some of the European countries, the percentage of children diagnosed as overweight and obese is high. However, this tendency is different depending on the country. The highest rates of obesity are observed in eastern and southern European countries [13]. In Malta and southern Italy overweight or obesity are diagnosed in 35% of children, whereas the same conditions are observed in 15% of cases in Scandinavia and in 12% in the Netherlands [15]. In the year 2000, a research that was carried out in Cracow, the third largest city in Poland, revealed that overweight and obesity were identified in 15.13% of boys and 11.79% of girls. During the 1971–2000 period, a gradual increase in overweight and obesity in children aged 7–18 years (n= 3,733) was observed. The most remarkable increase was registered in boys aged 7–12 (n = 859) and in girls aged 7–10 (n = 483) [6]. In many countries, including Poland, a gradual increase in the number of overweight and obese children was an incentive to carry out a research in order to determine the extent of adiposity in the young population. In Cracow, such a study was performed in a group of children aged 6– 13, inhabitants of the city proper as well as neighbouring rural areas. The purpose was to estimate the prevalence of overweight and obesity in preschool and school children with reference to gender and place of residence. Material and method At the end of 2008 and the beginning of 2009, a sample of 1,499 children aged 6–13 years, residences of Cracow and neighbouring rural areas, was selected. The examined group consisted of 748 boys (549 urban and 199 rural ones) and 747 girls (553 urban and 194 rural ones). The group of rural subjects comprised the children between the ages of 7 and 12 years. The urban research group encompassed 6-year-olds and 13-year-olds. The measurements were taken according to the Martin-Saller method [17]. The measurement of weight and height allowed the calculation of body mass index (BMI) for every examined child. BMI ¼ weight ðkilogrammesÞ=height ðmetresÞ2 The BMI is widely used to evaluate the incidence of overweight and obesity. In the case of adults, the ratio above 25 kg/m2 indicates overweight and above 30 kg/ m2—obesity. [14] BMI values estimated in children differ depending on gender and age of the examined subjects but the correlation Eur J Pediatr (2012) 171:245–251 is not the same as in adults [21]. Therefore, as far as children are concerned, it is best to use cut-off points applicable for children and adolescents that correspond with their age and gender. In the examination performed the prevalence of overweight and obesity in children was determined by means of the International Obesity Task Force cut-offs with respect to age [8]. This method is applied in many international research centres. It allows for a comparison of the results of the authors’ own research with the data provided in worldwide publications. Additionally, overweight and obesity values in girls were determined according to age groups corresponding with the degree of sexual maturity. They were divided into two age groups: childhood (7–10 years) and early adolescence (11– 13 years). Taking into consideration the difference in the pubertal progress in boys and girls, the division allows for other age categories: childhood and early adolescent. The examined subjects were grouped according to the criteria established by Chrzanowska et al. [6]. Statistical analysis Sex-related differences in all anthropometric indicators were analysed by the Student’s t test. The chi-square test was used to determine the differences between groups. The significance level was 0.05. The Mann–Whitney–Wilcoxon test (also called the Wilcoxon rank-sum test or W test) was used to determine whether the medians of the BMI in boys and girls included in data sets were equal. It was used instead of the Student’s t test in a case of non-normal distributions of variables. Results The comparison of body height in the examined subjects did not reveal any statistically significant differences in Table 1 Median values, ranges, mean values and standard deviation of weight and height in all boys and girls Number Med. Ranges Mean SD Boys Height [cm] Weight [kg] Girls Height [cm] Weight [kg] Med. median values, SD standard deviation All 748 747 140.0 35.0 138.8 33.8 103.5–177.0 16.1–106.5 103.3–170.7 16.1–83.0 139.9 37.3 139.2 35.5 12.9 11.58 13.9 11.19