The purpose of this study was to compare the first file that fits to the apex (FFFA) in each canal before and after early flaring to analyze if the size of file to fit to the apex would increase after flaring. One hundred mesial canals of lower first and second molars with complete apical formation and patent foramens were selected. The samples were randomly divided into two groups of 50 canals each. A file was fit to the apex in each canal and that size recorded. Radicular flaring was completed using Gates-Glidden drills in group 1 and Rapid Body Shapers in group 2. After flaring a file was again fit to the apex in the same manner as before and its size recorded. The mean diameter of FFFA before flaring (file diameters in mm x 10(-2)) was 14.46 (+/-4.12) and after 23.3 (+/-7.2) for group 1 (p < 0.001), whereas in group 2 the mean diameter of FFFA was 17.2 (+/-4.96) before and 25.6 (+/-6.36) after (p < 0.001). A Wilcoxon t test indicates a significant difference (p < 0.001) between the diameter of FFFA before and after flaring in both groups. The increase in diameter was approximately two file sizes for both groups. From this observation it is concluded that early radicular flaring increases the size file that is snug at the apex, and awareness of that difference gives the clinician a better sense of canal size. Early flaring of the canal provides better apical size information and with this awareness, a better decision can be made concerning the appropriate final diameter needed for complete apical shaping.