Objective:To evaluate the interference of active cellphones during electronic working length (EWL) determination of a root canal.Materials and Methods:Thirty patients requiring root canal treatment in the anterior teeth or premolars having single canal and mature apices were selected for this study. Working length determination was done using no. 15 K-file. Electronic apex locators ProPex Pixi and Root ZX mini were used for working length determination. Cellphones iPhone 6s and Xolo Q3000 were evaluated for their interference. The experiment was conducted in a closed room (9 feet × 9 feet). Working length was measured with no cellphone in the room, iPhone 6s in a calling mode, Xolo Q3000 in a calling mode, and Xolo Q3000 and iPhone 6s simultaneously in a calling mode. Stability of the readings was also determined for every condition.Statistical Analysis:The data were statistically analyzed using one-way ANOVA and paired t-test at 0.05 level of significance.Results:Results were not statistically significant.Conclusion:Within the limitations of the present study, cellphones do not interfere with the EWL determination.