Electronic apex locators (EALs), cone-beam computed tomography (CBCT), and radiovisiography (RVG) claim to determine of working length (WL) in primary molar teeth. To evaluate the accuracy of WL determination by using three EALs, RVG, and CBCT imaging in extracted human primary molar teeth with/without root resorption. Twenty extracted primary molar teeth with resorption and 20 extracted primary molar teeth without resorption were used. After measuring actual lengths (AL) (Group 1), the electronic WL measurements were performed by using three different EALs [COXO C Smart-1 Pro (Group 2), iPex (Group 3), and Apex ID (Group 4)]. Two different image sets were obtained as follows: CBCT imaging (Group 5) and RVG (Group 6). AL measurements performed with an endodontic measuring ruler and compared with the EAL, CBCT, and RVG image measurements. For all groups, there were no significant differences between the teeth with resorption and without. There were no significant differences in measuring methods from AL and between the methods used (p > .05). When electronic and radiographic method were compared in different frequency ranges, there was no statistically significant difference (p > .05). This study showed that EALs, CBCT, and RVG have high accuracy in primary molar teeth both with resorption and without root resorption and can be used for determining WL.