Full text article. Also available at https://doi.org/10.2147/OAS.S264176We aimed to determine the prevalence of and characterize accessory maxillary sinus ostium (AMO) in patients with chronic rhinosinusitis at a private health facility which serves the largest number of patients seeking treatment under private practice in Tanzanias largest city. Chronic rhinosinusitis is a common condition in otorhinolaryngology practice. It has been postulated in the available literature that accessory maxillary ostium may play a role in the development of chronic maxillary sinusitis. AMO has been frequently identified during routine nasal endoscopy. Its found in the medial wall of the maxillary sinus and located in the lateral wall of the nose. There is no study to date that has been conducted in Tanzania to characterize AMO in patients with chronic rhinosinusitis when seen at the clinic despite the growing use of endoscopy on an outpatient basis. Fifty adult patients with symptoms of chronic rhinosinusitis attending the ENT clinic on an outpatient basis were selected and then computerized tomography scan of the nose and paranasal sinuses (CT scan PNS) was performed. Nasal endoscopy was done to all patients to determine the presence and location of AMO. Of all the 50 studied patients, CT scan PNS depicted positive signs of rhinosinusitis in 35 patients (70%). Upon nasal endoscopy of the 35 patients, AMO was found in 25 patients (71.4%). Of the 15 patients with no depicted CRS upon CT scan, AMO was found in 4 (26.7%) patients. Nasal endoscopy provides additional evidence of obstruction of natural sinus ostia thus leading to chronic maxillary rhinosinusitis apart from CT PNS. Such observation is of importance to clinicians who are to execute management of these patients.