The fracture of rotary nickel-titanium instruments is an unfortunate incident that might complicate and compromise the outcome of endodontic treatment, especially if adequate cleaning and shaping and/or proper sealing cannot be achieved in infected root canals. A great deal of research has been carried out to try to understand the reasons for instrument fracture and how it may be prevented rather than treated. The purpose of this review is to discuss the factors that might influence the performance and clinical safety of rotary nickel-titanium instruments. Keywords: endodontic treatment, instrument fracture, rotary, nickel-titanium