Peak height velocity (PHV) is defined as the period of the fastest growth during puberty. An ability to predict annual growth and the timing of PHV may provide an opportunity to modify treatment of many diseases and conditions of the skeletal system such as scoliosis and kyphosis, slipped capital femoral epiphysis, leg length inequality and adolescent Blount's disease. There is a good correlation of peak height velocity and skeletal age determined from the radiographic assessment ofolecranon. To avoid radiation, we tested value of olecranon ultrasound in prediction of annual growth and peak height velocity. In present study, using ultrasound, we made a classification of olecranon apophysis in 7 levels (0-6) according to the amount of cartilage left unossified. In 134 healthy children, aged from 10 to 15, evaluation of olecranon sonographs and staging was done by two observers in two spaced time intervals. Calculation of intra-examiner and inter-examiner agreement presented satisfactory reliability (intraclass correlation coefficient for Rater 1 = 0.967 and Rater 2 = 0.836) and very good reproduciblity (Cohen's Kappa 0.85). We measured increase in height, during six month period, for 54 children, who were classified by ultrasound in levels from 0 to 6. The greatest growth was noted in children classified as level 4. Olecranon apophysis maturity level 4, assessed by ultrasound could correspodent to peak height velocity.