Based on the results obtained in previous studies, principles and techniques in the operative procedure of endodontic surgery are discussed. It is stressed that periapical surgery in itself is no cure for periapical inflammation. The main object of periapical surgery is to enable a complete debridement and a tight root filling to be made. The access to both ends of the root canal should be utilized in the root filling technique. Root filling should therefore be made during the operation. If the root has been filled previously, a new root filling should be made. It often may be advantageous to open into the canal through the crown, after the root apex has been exposed. If resection of the root will improve the efficiency of the root filling, this should be done. Otherwise, the whole root length should be retained to provide maximum support for the tooth. Periapical soft tissue should be removed because it may contain epithelium which may develop into a cyst or proliferate to cover the root surface. In the present series no attempts were made to sterilize the root canal before filling, but all efforts were concentrated on removing necrotic tissue from the canal and establishing a tight root filling. The results obtained after this method were at least as good as in cases reported in the literature where a bacterial control showed sterility of the root canal before filling. Periapical surgery is indicated in those cases in which conservative endodontic therapy cannot be carried through, or where the efficiency of a root filling can be improved. Further indications are if a cyst or acute periapical inflammation is present. Only few contraindications exist and complications after periapical surgery are rare.