Aim: To investigate the type of defects in Reciproc Blue 25 instruments after clinical use by a single endodontist. Materials and method: A total of 47 Reciproc Blue R25 instruments used by a single endodontist that were discarded from the endodontic clinic after five molar teeth treatments were collected over 4 months. They were ultrasonically cleaned, autoclaved, and then examined in the laboratory under stereomicroscope x2,5, and x4 magnification to determine the distortion and separations. The instruments were classified as 1:fracture1: fracture, 2:unwinding2: unwinding, and 3: no visible defects unfractured. The fractured files were categorized into torsional or flexural failure. Those that had fracturedfractured, and unwinding files were analyzed for plastic deformation in lateral view and fractographic examination in fracture end with the scanning electron microscope. Results: Approximately 6,3% of all discarded Reciproc Blue R25 instruments were fractured, there were no visible defect on 86,3% of the files. About %4,2 of instruments failed because of tortional fracture and 2,1% of instruments failed because of flexural failure. TorsionalThe torsional fracture occurred in 66,6 % of all fractured files, whereas flexural fatigue occurred in 33,3%. Conclusions: Within the limitations of this study, the risk of fracture of the Reciproc Blue R25 file was found to be low when using up to 5 molars by a single endodontist.