Objective. To evaluate the influence of various factors on the success or failure of attempts to remove fragments of separated NiTi instruments from root canals. Study design. Instrument removal attempts were undertaken on 72 teeth with a separated NiTi instrument using a variety of techniques and armamentarium. Factors including type of tooth, degree of root canal curvature, location of fragment in relation to the root canal curvature, and radiographic length of fragment were analyzed. A success of treatment was defined as removal or complete bypassing of the fragments. Results. The overall success rate was 53%. The success rate for ProFile fragments was 41% and for the NiTi K-file 60%. The success rate in maxillary teeth was higher than that in mandibular teeth. Of 52 instruments in molars, 28 were successfully removed or bypassed. Of the 12 fragments in premolars, only 2 were removed. All 8 cases in anterior teeth were retrieved completely. When the fragment was localized before the curvature, complete removal was achieved. When the fragments were located at and beyond the curvature, the success rates were 60% and 31%, respectively. In canals with a slight, moderate, and severe curvature, the success rates were 100%, 83%, and 43%, respectively. In general, the longer the fragment, the greater the chance for successful removal or bypass. Conclusions. Favorable factors for removal of separated NiTi fragments are straight root canals, anterior teeth, localization before the curvature, fragments longer than 5 mm, and hand NiTi K-file.