The morphology of the sphenoid air sinuses is variable amongst populations. The variation in terms of the morphology of this air sinus is particularly important in cranial base surgery. This study aimed to illustrate the three dimensional (3D) morphology of the sphenoid air sinus across ages 1 to 25 years in a South African population. The frequency of the sphenoid sinus characteristics viz. its presence, shape and septa was observed in 3D reconstructed sphenoid sinus models. The sample (n=480

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... atients) consisted of 276 males and 204 females, 1-25 years and of two population groups viz. black African and white. The sphenoid air sinus was present in (442/480) 92.1 % on the right and in (441/480) 91.9 % on the left. The sphenoid air sinus was absent in 7.9 % and 8.1 % on the right and left sides respectively. Of those present, six different shapes were identified in the anterior/coronal view. Overall, the main shape identified in the anterior view, was quadrilateral on the right (n=243; 50.6 %) and left (n=238; 49.6 %). There was no association between the shape anteriorly and sex or population groups. However, three forms in the lateral view viz. sellar, presellar and conchal types were documented. The main shape identified was the sellar type on both sides (45.2 % R; 49 % L). Laterally, there was an association between shape and sex, on the left side only, and, between the population groups (p<0.05). Intersinus septa were observed in 90.2 % and located predominantly central in 55.4 %. The maximum amount of partial intrasinus septa observed was up to 7 septa. An in depth analysis and classification of the three dimensional form of the sphenoid air sinus according to age 1-25 years was documented in this study. This study proposed a classification of the air sinus utilizing its three dimensional form. The classification illustrated how the air sinus developed within the sphenoid bone and grows into its surrounding parts in both a lateral and posterior direction.