The aim of this in vitro study was to compare the centring ability of the ProTaper™ and ProTaper Universal™ rotary systems for preparing curved root canals, by means of preoperative and postoperative imaging of a cross-section of their coronal, middle and apical thirds. Twenty mesiobuccal root canals of human mandibular first molars with a degree of curvature ranging from 55° to 60° were randomly divided into two groups of 10 specimens each: Group 1, ProTaper™ rotary system; and Group 2, ProTaper Universal™ rotary system. The data were analysed statistically by Kruskal–Wallis and Student’s t-test at the 5% significance level. The results showed that the differences between the percentages of the presence of deviation observed were not statistically significant. Both systems showed the capacity for producing centred preparations in curved root canals with low proportions of deviation.