Of the various techniques used to determine the optimum timing for growth modification treatments, the cervical vertebrae maturation method has great advantages, including validity and no need for extra X-ray exposure. Recently, the reproducibility of this method has been questioned. The aim of this study was to investigate the cause of poor reproducibility of this method and to assess the reproducibility of the clinical decisions made based on it. Seventy lateral cephalograms of Iranian patients aged 9‒15 years were observed twice by five experienced orthodontists. In addition to determining the developmental stage, each single parameter involved in this method was assessed in terms of inter- and intra-observer reproducibility. In order to evaluate the reproducibility of clinical decisions based on this method, cervical vertebrae maturation staging (CVMS) I and II were considered as phase 1 and CVMS IV and V were considered as phase 3. By considering the clinical approach of the CVMS method, inter-observer reproducibility of this method increased from 0.48 to 0.61 (moderate to substantial) and intra-observer reproducibility enhanced from 0.72 to 0.74. 1. Complete visualization of the first four cervical vertebrae was an inclusion criterion, which also limits the clinical application of CVMS method. 2. These results can be generalized when determining growth modification treatments solely for Class II patients. Difficulty in determining the morphology of C3 and C4 leads to poor reproducibility of the CVMS method. Despite this, it has acceptable reproducibility in determining the timing of functional treatment for Class II patients.