Objective: To evaluate in cochlear implant patients, the feasibility and reliability of angular depth of insertion (aDOI) measurements using plain x-ray scans.Study Design: Retrospective study where three observers independently evaluated and compared intraoperative anterior-posterior and oblique x-ray scans.Setting: A tertiary pediatric medical center.Patients: Included were 50 children (100 ears) who underwent bilateral simultaneous cochlear implantation during 2008 to 2015.Main Outcome Measures: Inter-rater agreement of aDOI measured in plain x-ray scans; effect of head position on measured aDOI; and symmetry of aDOI between patients' ears in bilateral simultaneous cochlear implantations.Results: Differences in the average aDOI measurements among the three observers ranged between 2 and 7 degrees. There was high inter-rater agreement (R = 0.99, p < 0.01) among all observers, and strong correlations between each pair of observers (0.92-0.99). Head rotation of 45 degrees (between the two views) resulted in a median difference in aDOI of 14 degrees, with excellent correlation among the observers. The rate of asymmetry was high, with a median difference of 39 degrees and up to 220 degrees between ears.Conclusions: Assessment of aDOI using intraoperative plain x-rays is efficient and reliable. The effect of head positioning on measurement is small. Further studies are needed to evaluate the effect of aDOI and insertion symmetry on functional outcomes.