AbstractBackgroundWorking length is an important step in primary teeth pulpectomy.AimTo evaluate whether there is a significant difference in the accuracy of electronic apex locators compared to the conventional radiography in working length measurements.DesignSixty‐four children (192 canals) between 5 and 9 years of age with indication for pulpectomy of a primary molar were included after eligibility criteria. A radiographic measurement was obtained from pre‐operative radiography from the cusp tip to the apex or resorption of the root. The electronic measurement was obtained from a complete measurement of the canal with an electronic device up to the apex. Data were analysed with Bland‐Altman plots and Wilcoxon test. Statistical significance was set at P ≤ .05.ResultsStatistically, there is not any significant difference between radiographic and electronic measurements for the palatal canal or distal canal, as well as mesiobuccal canals (P > .05). Statistically, there, however, is a significant difference between the measurements for the distobuccal canal and mesiolingual canal measurements (P < .05). High internal consistency for both radiographic and electronic methods was achieved (α ≅ 1).ConclusionsElectronic and radiographic methods are similar in determining the length measurement of the root canals in primary teeth pulpectomies, except in distobuccal or mesiolingual canals.