OBJECTIVE To assess the fusion patterns of the spheno-occipital synchondrosis (SOS) in the age range of 9-22 using CT and CBCT images of an Iranian population. METHODS Spiral CT and CBCT scans of 763 subjects (459 males and 304 females) aged 9-22 were evaluated. The scans had to cover the cranial base area, and those with diseases affecting the bone density, cranial base masses and history of trauma were excluded. METHODS Two oral and maxillofacial radiologists scored the images with regard to the status of SOS fusion based on a 5-stage system. Mann-Whitney, Kruskal-Wallis and Fisher's exact tests were used for data analysis. Age and SOS fusion stages were evaluated through Spearman correlation and linear regression methods (α = 0.01). RESULTS The earliest age for onset of SOS fusion was 9 in both sexes. Open SOS could be observed until the age of 15 and 14 in males and females, respectively. The earliest age of complete fusion was 12 in males and 13 in females. Furthermore, there was a significant, positive correlation between age and the different stages of SOS fusion (P < .001). CONCLUSIONS A significant correlation exists between age and the fusion stages of SOS, rendering it an appropriate means of age estimation during growth periods. Fusion of SOS begins approximately 2 years earlier in females; however, it ends at the age of 17 in both sexes. The fusion scar can be detected up to the age of 12 and 13 in males and females, respectively.