PURPOSE: A polymorphism in the IGF-I gene promoter region is known to be associated with serum IGF-I levels, birth weight, and body length, suggesting that IGF-I gene polymorphism might influence postnatal growth. The present study aimed to investigate the role of this polymorphic cytosine-adenine (CA) repeat of the IGF-I gene in children with idiopathic short stature. METHODS: The study involved 131 children (72 boys and 59 girls) diagnosed with idiopathic short stature, aged 7-15 years. Genomic DNA was extracted from anticoagulated peripheral whole blood. The primers were designed to cover the promoter region containing the polymorphic CA repeat. Data were analyzed using GeneMapper software. The correlations between age and serum IGF-I levels were analyzed using Spearmans correlation coefficient. RESULTS: The CA repeat sequences ranged from 15 to 22 , with 19 CA repeats the most common with an allele frequency of 40.6%. Homozygous for 19 CA repeat was 13.0%, heterozygous for 19 CA repeat was 56.5%, and 19 CA non-carrier was 30.5%. The three different genotype groups showed no significant differences in height, body weight and body mass index, and serum IGF-I levels. The serum IGF-I level and age according to the IGF-I genotypes were significantly correlated in the entire group, 19 CA repeat carrier group, and the non-carrier group. The three groups also showed no significant differences in the first year responsiveness to GH treatment. CONCLUSION: There were no significant different correlations between 19 CA repeat polymorphism and serum IGF-I levels according to genotype. Our results suggest that the IGF-I 19 CA repeat gene polymorphism is not functional in children with idiopathic short stature.