Computed tomography was used to evaluate root canals prepared by nickel-titanium (Ni-Ti) hand and stainless steel hand endodontic instruments. Thirty-six single-rooted teeth of similar shape and canal size were divided into three groups. The teeth were scanned by computed tomography before instrumentation. In group A, canals were instrumented using a quarter turn/pull technique with K-flex files. In group B, canals were prepared with Ni-Ti hand files (Mity files) using the same technique as group A. Group C was prepared with Ni-Ti hand files (Mity files) using a reaming technique. Instrumented teeth were again scanned using computed tomography, and reformated images of the uninstrumented canals were compared with images of the instrumented canals. Ni-Ti instruments (Mity file) used in a reaming technique caused significantly less canal transportation (p < 0.05), removed significantly less volume of dentin (p < 0.05), required less instrumentation time (p < 0.05), and produced more centered and rounder canal preparations than K-flex stainless steel files used in a quarter turn/pull technique. The computed tomography imaging system used in this study provided a repeatable, noninvasive method of evaluating certain aspects of endodontic instrumentation.