The determination of skeletal age is essential in the management of patients with scoliosis. One of the most frequently used techniques to determine skeletal maturity is the method described by Risser. However, repeated X-ray exposure in the follow-up examinations of scoliosis patients may increase the risk of cancer. We compared conventional radiological evaluation of the Risser grade with ultrasound evaluation. For scoliosis patients routine application of ultrasound in the follow-up examinations may significantly reduce radiation exposure. 46 adolescent idiopathic scoliosis patients (median age, 14.5 years) were investigated. Sonographic and radiographic assessment of Risser sign was carried out by two independent senior staff skeletal radiologists. Agreement of Risser Grade between the two diagnostic methods was determined by Kappa statistics. Coefficients <0.21, 0.21-0.40, 0.41-0.60, 0.61-0.80, and >0.80 were rated as poor, fair, moderate, good, and very good agreement. For Risser Grades I-III 100% agreement was found between the two methods. Disagreement between radiographic and sonographic evaluation was found in Risser Grades IV and V. In five patients, X-ray evaluation yielded Risser Grade V while ultrasound showed Risser Grade IV. In one patient, radiographic examination resulted in Risser Grade IV while Grade V was detected in ultrasound. Overall, the Kappa value showed very good agreement between the two diagnostic methods. Our findings suggest that ultrasound can be applied as an alternative method to X-ray evaluation in Risser Grade determination. It should be routinely used in clinical practice to reduce the patients exposure to radiation.