An osteoplastic modification of the Caldwell-Luc operation is described. Starting from two small drill holes a quadrangular lid is cut out of the anterior wall of the maxillary sinus using the reciprocating micro-saw after Feldmann. This allows adequate access to the cavity as in the classic procedure. If required the window can be extended in the superior medial angle with rongeurs. After completing the operation within the cavity the osseous lid is reimplanted and fixed with 3 sutures of chromic catgut, which are threaded through small drill holes. By this prodecure prolapse of fat into the sinus is prevented, postoperative closure of the antral nasal window is less likely to occur, the bony structure of the maxilla is restored. Keeping of the reimplant presents no problem. Sequestration or other complications have not been encountered either in suppurative or in polypous sinusitis.