Achondroplasia, the most common form of skeletal dysplasia in man, has autosomal dominant inheritance and causes severe dwarfism. More,than 90% of patients with achondroplasia, have a G to A transversion or G to C transversion at position 1138 of the fibroblast growth factor receptor-3 (FGFR3) gene resulting in the substitution of an arginine for a glycine residue at position 380 (G380R) of the FGFR3 protein. In this study, 12 unrelated Turkish patients with achondroplasia were evaluated for the G to A and G to C transversion at position 1138 of the FGFR3 gene. Eleven of 12 patients carried the G to A mutation heterozygously. None of the patients had the G to C mutation at the same position.