From September 1992 to March 1994 at the Department of Oral Surgery of the Dental School of the University of Vienna a total of 218 microsurgical apicoectomies and ultrasonic retro-preparations were carried out in 142 patients. Among other indications for operation was the failure of previous surgical-endodontic procedures in 62 cases. In 51 teeth (82%) of these patients the cause of failure could be evaluated with the help of the microscope. Twelve teeth (19%) extracted afterwards showed a longitudinal root fracture which had not been diagnosed before. In all other teeth retro-preparation and filling with zincoxide-eugenol cement was possible, even in cases of difficult anatomic approach. Due to the excellent experiences with microsurgical technique in apicoectomies, the use of the microscope in other fields of dental surgery remains only a matter of time.