Background: Chronic suppurative otitis media has remained prevalent in most developing countries including Nigeria with plain mastoid radiograph still playing a part as an investigation tool in patients with this disease. Aim: To determine the pattern of mastoid pneumatization in patients with uncomplicated chronic suppurative otitis media using plain radiograph of the mastoid. Methodology: This was a prospective hospital based study, which was carried out in the Otorhinolaryngology clinic and Radiology Departments of Aminu Kano Teaching Hospital, Kano. All first attendees that presented with symptoms and signs of chronic suppurative otitis media whose investigations included plain mastoid radiograph and met the inclusion criteria were enrolled into the study. Quantitative measurement of the mastoid air cells was obtained from the radiograph using mastoid planimetry. The collected data was entered into the computer and analyzed using Statistical package for Social Sciences (SPSS) Version 15 and Minitab 12.0. Results: A total of 121 patients enrolled in the study. There were 62(51.2%) males and 59(48.8%) females. Their ages ranged from 5 - 80 years (mean=19 years ± 14 SD). They were mainly students (66.6%) who presented with ear discharge (100%), hearing impairment (100%), tinnitus (59.6%), otalgia(1.6%) and vertigo (2.5%). The examination findings were mainly Tympanic Membrane perforation and Conductive Hearing Loss (100%) demonstrated. The mean area of mastoid air cells were: 4.7cm2 and 12.97cm2 in the diseased and normal ears respectively; with a prevalence of sclerotic or poorly pneumatized mastoid ranging from 59.8-62.5% (diseased ear) to 2.9-8% (non-diseased ear). There was significant correlation between the disease and mastoid pneumatization (P<0.05). Similarly, mastoid pneumatization pattern correlated well with the duration of the disease (P<0.05). On the contrary, sex, age and the side of the ear affected had no correlation with mastoid pneumatization. Conclusion: CSOM is associated with high prevalence of poorly pneumatized mastoid, which is made worse by prolonged duration of disease and thus an evidence for the environmental theory of mastoid pneumatization and may be a possible indicator of a difficult mastoidectomy.