Osteomas are benign bone tumors, which are mostly localized in the nasal sinuses. The removal of nasal sinus osteomas, because of their hardness and scope, mostly requires extensive drilling work, which, especially in the case of big osteomas, also makes a large access path necessary. The introduction of endoscopic or microscopic technologies and experiences from the endoscopic opening of the osseous choanal atresias, where extensive drilling deep in the nose is carried out, make the endonasal access possible, even for the removal of nasal sinus osteomas. We treated a 59 year old patient, who, beside a pronounced polyposis of the nasal sinuses, also exhibited a large osteoma in the area of the right ethmoidal labyrinth. In the course of the intranasal sinus operation, the osteoma was completely removed via the same access route. The osteoma had to be gradually minced, intranasally, as it was too large to pass through the piriformes aperture. This approach shows an expansion of our endoscopic possibilities. Additionally, the etiology of the osteoma and its correlation with the polyposis is discussed.