Objectives The estimation of skeletal maturity is a useful tool in pediatric practice to determine the degree of delay or advancement in growth disorders and the effectiveness of treatment in conditions that influence linear growth. Skeletal maturity of children is commonly assessed using either Greulich–Pyle (GP) or Tanner–Whitehouse methods (TW2 and TW3). However, a less invasive ultrasonic method, that does not use ionizing radiation, has been suggested for use in epidemiological studies of skeletal maturity. The main purpose of the present study was to determine the accuracy of an ultrasonic method based on the GP maturity indicators compared to the standard GP radiographic method. Methods Skeletal maturity of 1502 healthy children, aged from 6 to 18 years, was estimated by quantitative ultrasound and compared to GP bone ages estimated from left hand and wrist radiographs of a subsample of 47 randomly selected participants. Results The ultrasonic bone age estimation demonstrated very strong correlations with all the radiological age estimations. The correlation coefficients ranged between 0.895 and 0.958, and the strongest correlation of ultrasonic skeletal maturity estimation was found with the Tanner–Whitehouse RUS method. The ultrasonic bone age estimation is suggested for use between the chronological ages of 8.5–16.0 years in boys and 7.5–15.0 years in girls. Conclusions The ultrasonic bone age estimation is suggested for use in epidemiological surveys since the sensitivity for screening for not normal bone development is appropriate, at least within the 8–15 years age interval.