Sitting height (SHt) measurements and sitting height/height (SHt/Ht) ratio are important criteria in the diagnosis of growth problems and particularly in the diagnosis of dysproportionate growth. It is known that body proportions are related to genetic influences and show variations among different populations. This study aimed to provide reference data on SHt and SHt/Ht ratios for Turkish children of ages 6-18 years. SHt measurements were performed on a sample of 1,100 boys and 1,020 girls between 6 and 18 years of age attending primary and secondary schools located in six different districts of Istanbul city. Criteria advanced by WHO for establishing reference standards for growth were observed in the study design. The sample consisted of a mixture of children measured only once and those measured at follow-up over different periods of time. Parallel to increase in Ht, SHt increased with age. Mean value for SHt/Ht ratio was 55-56 % at ages 6 to 8.5 years in both sexes. In girls, this value started to decrease at age 11.5 years and remained between 53 % and 54 % thereafter. In the boys, a decrease to 52-53 % was noted in the SHt/Ht ratio after age 12 years. In both sexes, SHt/Ht ratio decreased with puberty, demonstrating that growth in trunk length exceeded growth in limb length in midpubertal ages. These changes occurred at an earlier age in the girls. Values obtained for SHt/Ht ratios in Turkish children were high as compared to Dutch children and low as compared to Chinese children. Conclusion: This study, by providing reference data on sitting height and sitting height/height ratios in Turkish children of ages between 6 and 18 years, will be useful in the diagnosis and follow-up of children with growth problems. This study also supports the view that body proportions are influenced by genetic makeup.