To evaluate the developmental status of children and adolescents, a bone-age chart based on the radiograph of hand and wrist has been used in many countries. 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 the height-weight-age table. As a standard bone-age chart has not been established in Korea, a foreign bone-age chart has been used in clinics. To make a Korean standard bone-age chart, we took the radiographs of the left hand of about 5,400 children covering the whole country, and 3,407 radiographs of 1,830 boys and 1,577 girls ranging from two months to 16 years of age were selected and analyzed for bone maturity scores by the TW2-20 method. The range of ages 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 a Korean standard bone-age chart can be used as the radiological index in the evaluation of the developmental status in Korean children and adolescents.