Abstract: Introduction and objective: The mastoid air cell system represents a more or less extensive system of interconnecting air filled cavities arising from the mastoid and walls of middle ear. Based on the density of mastoid air cells it has been described as sclerotic (absence of pneumatisation), diploic type (partially pneumatised), pneumatic (totally pneumatised). The pneumatised type were further described as squamomastoid, perilabrynthine, petromastoid and accessory (occipital). The knowledge regarding the status of pneumatisation of mastoid process is very essential for otologists while performing surgeries like cochlear implant, drainage of mastoid abscess, middle ear surgeries Materials and method: In the present study 50 dried skulls of south Indian origin (males =28 , females = 22) of age more than 50 yrs were studied in detail by computerized tomography. Hence details regarding pneumatisation were observed in 100 mastoid processes. The extent and type of pneumatisation were recorded and analysed. Results: observations revealed incidence of squamamastoid type was seen in 74 cases, petromastoid type in 12 cases, perilabrynthine in 12 cases , sclerous type in 2 cases and accessory nil. Conclusion: Mastoid process is frequently approached by otologists to perform mastoidectomy, cochlear implant placement in neural deafness and in some of the middle ear surgeries.