Using an endoscope in periradicular surgery provides an impressive optical enlargement and may lead to better clinical diagnostics and a high rate of success. Aims of this investigation were examining this hypothesis as well as detecting influencing factors. In 2002 and 2003, 114 teeth of 91 patients were root-end resected using endoscope. Before surgery, the tooth, number of resected root-ends, content of root channels, clinical diagnosis and moment of surgery were recorded. Patients were controlled one year after surgery and success was evaluated as a summary of clinical and radiological findings. Four patients did not reappear for the control examination. Out of 110 teeth, treatment was successful in 91.8% and failed in 7.3%. 0.9% could not be classified. Statistically, more failures were noted after periradicular surgery in molars. The rate of success increased during the study by means of a learning curve. The results confirm the hypothesis that where using an endoscope periradicular surgery is highly successful.