A comparison between the results obtained from X-ray examination and endoscopy (sinoscopy) of the maxillary sinus has not previously been published. In the present series 585 maxillary sinuses were examined by both methods. In 3 % of the cases we were unable to accomplish sinoscopy, and in 9% we may have overlooked the changes seen on the X-ray pictures. Sinoscopy was superior to the X-ray examination in the remaining cases, giving more exact information for differential diagnosis of the type and degree of the changes found in the sinus. An exact diagnosis by X-ray was not obtained in 29% of the sinoscopical diagnoses, although this could reasonably have been expected. The presence of discharge was incorrectly diagnosed at X-ray examination in 38% of the cases. Sinoscopy can give valuable information in cases of malignancy of extension to the maxillary sinus prior to irradiation or surgery. Consequently, in many cases one must consider whether the standard X-ray examination of the sinus can be replaced by sinoscopy. Acta Otolaryng 74Acta Otolaryngol Downloaded from informahealthcare.com by McMaster University on 12/26/14 For personal use only. Acta Otolaryngol Downloaded from informahealthcare.com by McMaster University on 12/26/14 For personal use only. Acta Otolaryrig 74 Acta Otolaryngol Downloaded from informahealthcare.com by McMaster University on 12/26/14 For personal use only. Acta Otolaryngol Downloaded from informahealthcare.com by McMaster University on 12/26/14 For personal use only.