Objectives: The objective of this study was to compare the step-down technique in simulated curved root canals using K hand files (VDW) and ProFiles 0.06/0.04 (Dentsply Maillefer). Method and Materials: A total of 72 canals were blindly prepared by instructed students: 1 block with K files and a second one with ProFiles 0.06/0.04 in connection with the EndoStepper (SET). Postoperative images of the canals were taken, and an independent dentist assessed preparations for amount and position of material removed during preparation. Efficacy of the instruments is described in terms of canal shape, instrument failure, canal blockages, and preparation time. Results: ProFile instrumentation provided well-centered and tapered preparations while maintaining the apical foramen; in contrast, the use of K files resulted in frequent alterations of the root canal. In the apical portion, both techniques showed unprepared areas. The coronal diameter in hand-instrumented canals was more irregular and wider than in those mechanically prepared. There was no separation of a ProFile instrument. Hand instrumentation was faster than mechanical, but the difference was not statistically significant. Conclusion: Under the conditions of the study, the ProFile rotary system was simple and safe to use and created better preparations than hand instrumentation. Keywords: hand instrumentation, mechanical preparation, nickel-titanium, rotary, simulated root canals