To evaluate the developmental status of children and adolescents, bone-age chart based on the radiograph of hand and wrist has been used in many countries. The bone-age reflects not only the functional status of various hormones but also the influence of chronic disease, and it has been used more widely than other indices such as height-weight-age table. As the standard bone-age chart has not been established in Korea, the foreign bone-agechart has been used radiographs in the clinics. To make Korean standard bone-age chart, we took the radiographs ofthe left hand in about 5400 children covering the whole country, and 3407 radiographs of 1830 boys and 1577 girls ranging from two months to 16 years of age were selected and analyzed for bone maturity scores by TW2-20 method. The range of age were divided into 27 groups, and the radiographs of 50th percentile score were chosen as the standard bone-ages for the median age of each group. The youngest and oldest chronological age which had the same TW2-20 score of the standard bone-age were decided as the range of variation from the median age. we hope that Korean standard bone-age chart be used as the radiological criteria in the evaluation of the developmenta status in Korean children and adolescents.