The prevalence of obesity in child population is becoming a serious problem in all advanced countries. Therefore many authors try to find a definition according to which it would be possible to assess overweight and obesity in examined subjects in a simple manner. The simplest way is to plot the subject's data in a percentile zone of reference data according to his BMI value. The problem is dealt with e.g. by Cole et al. (1) who defined internationally acceptable standards of BMI for children and adolescents from 0-18 years. These standards are, however, based only on six national studies and on the assumption that in the population of 18-year-olds there are 10% subjects with BMI values above 25 and 3% subjects with values above 30. The suggested standards thus raise the level of the 90th and 97th percentile, as compared with BMI reference data of 1991 which are used in the Czech Republic. Therefore the ratio of obese children in the Czech Republic and in many other countries would be very small. Internationally acceptable standards should be therefore based on a broader discussion of the professional public.