Abstract: Objective: Investigate the relationship between the mastoid pneumatization and the paranasal sinus volumes in patients with unilateral chronic otitis media (COM) and make a contribution to understanding of COM etiopathogenesis. Methods:101 patients were divided into two groups: group 1, COM with isolated tympanic membrane perforation, consists of 51 patients and group 2, COM with cholesteatoma/retraction pocket, consists of 50 patients. Mastoid and sinus volumes were evaluated on preoperative temporal bone High-Resolution Computed Tomography (HRCT). Results: Sphenoid sinus volumes were significantly lower at the diseased side (p< 0.05), while there is no statistically difference in the maxillary and frontal sinus volumes. Also, the sphenoid sinus volumes significantly lower at the side of the ear with sclerotic mastoid than others (p<0.001). Conclusions: Long-standing childhood COM might restrict to pneumatization of the same sided sphenoid sinus considering the delayed development of the sphenoid sinus compared with other sinuses.