Background. Mucocoele is histopathologically benign, cystic change of paranasal sinuses filled with mucoid contents, which with its growth is pressuring and destroying local bone walls. In only 3% of the cases it can be localized in maxillary sinuses. Etiology is unknown. Pyocoele develops by secondary infection. Case report. The male patient was 21 years old. His symptoms were runny nose with thick contents and heavy breathing on the right side of the nose, headaches, as well as the swelling of the right cheek. During clinical examination, the expansive change was found. It was completely closing the right side of the nose cavity. Computerized tomography (CT) of paranasal cavities showed excessive expansion of the right maxillary sinus, with very thinned walls, while the cavity was filled with liquid. After antibiotics therapy, the radical operation of the right maxillary sinus was performed, based on Caldwell Luc method. The frontal wall was found to be extremely convex and thinned, while the medial wall was with dehiscention. The cystic change was extirpated. Mucocoele was proved by pathohistologic findings. Its wall was about 2 mm thick and it showed squamous metaplasia in the large part of the mucocoela epithel. In the submucosa fibrosis and inflammatory infiltrate was present. Postoperative follow-up was under control. Clinically and radiographycaly, six months after therapy, the patient does not have troubles. Conclusion. The rare localization of the mucocoeles in maxillary sinus can be explained with the width of the maxillary ostia. Infected mucocoeles, expanded to the local anatomical structures, should be operated on with classic radical surgical operation. .