To evaluate the patency of the aditus ad antrum in cases of tubotympanic chronic suppurative otitis media (CSOM) and to measure its dimensions. Also, to examine its mucosa histologically for the presence of granulation tissue or occult cholesteatoma. Prospective case series. Main Alexandria University Hospital (tertiary referral center). Fifty adult patients with tubotympanic CSOM without evidence of cholesteatoma, after adequate medical control of otorrhea, presented with mild or moderate conductive hearing loss. In all patients, tympanoplasty with cortical mastoidectomy was performed. The patency and dimensions of the aditus ad antrum were assessed using a 30° endoscope. Biopsies were obtained from unhealthy mucosa to detect the presence of granulation tissue or occult cholesteatoma. Ten cases (20%) had a blocked aditus ad antrum by unhealthy and edematous mucosa. Biopsies revealed granulation tissue in all cases. No occult cholesteatoma was detected. The results were further analyzed in relation to multiple variables to detect any clinical clues of a blocked aditus. Of the studied cases, 20% had a blocked aditus. The prevalence of an obstructed aditus was higher among older patients with a long history (>1 year) of ear discharge. Marginal and subtotal central perforations and the presence of myringosclerosis increase the probability of an obstructed aditus ad antrum.