Aim:To evaluate the discrepancies between the diameter of the canal and the first file to bind at the working length, before and after preflaring in teeth with apical curvatures.Materials and Methods:Twenty teeth with apical curvatures were selected for the study. Following access, the patency file was fixed at the working length, and the apices were ground perpendicular to the canal at this level. Diameters of canal and the first file to bind at the working length were observed for each tooth, both before and after preflaring, under stereomicroscope at 30X magnification.Results:ANOVA and post hoc Bonferroni tests showed significant differences in both groups regarding anatomical diameter at working length and the first file to bind. The area of contact of the file at apical region remained the same in both groups.Conclusion:Using the first file to bind for gauging the diameter of the apical canal was found to be an unreliable method in teeth with apical curvatures, even after preflaring.