Objective - to study whether there is a need for uncinectomy for an access to the natural maxillary ostium. Material and methods. Ten cadavers (20 sides) were examined by maxillary ostial probing under edge endoscopic guidance, followed by uncinectomy and examination of the ethmoidal infundibulum with a 45° endoscope. Thirty patients underwent endoscopic maxillary reoperations, during which the uncinate process was removed and the ethmoidal infundibulum examined; the authors determined how successful the previous dilatation of the natural maxillary ostium was. Results. Cadaveric examination using 0, 30, 45, and 70° endoscopes and an Acclarent CyclopsTM multi-angle endoscope could not visualize the maxillary ostium in 19 of the 20 cases. Maxillary ostial probing under 0° endoscopic guidance proved unsuccessful in 55% of the cases, which indicated further uncinectomy and examination using the angle endoscopes. Endoscopic paranasal reinterventions revealed that an accessory maxillary ostium had been formed during previous interventions in 12 of 30 cases. At the same type, the natural maxillary ostium remained intact. Conclusion. During maxillary surgery, the application of an accessory ostium in the middle nasal passage without enlarging the natural ostium is an urgent problem. This is due to the use of edge optics during maxillary ostial probing and with uncinate process preservation or inadequate removal.