Study Design: Global Survey Objective: To determine the accuracy, interobserver reliability, and intraobserver reproducibility of the AO Spine Upper Cervical Injury Classification System based on surgeons’ AO Spine region of practice (Africa, Asia, Central/South America, Europe, Middle East, and North America). Methods: A total of 275 AO Spine members assessed 25 upper cervical spine injuries and classified them according to the AO Spine Upper Cervical Injury Classification System. Reliability, reproducibility, and accuracy scores were obtained over two assessments administered at three-week intervals. Kappa coefficients (ƙ) determined the interobserver reliability and intraobserver reproducibility. Results: On both assessments, participants from Europe and North America had the highest classification accuracy, while participants from Africa and Central/South America had the lowest accuracy (P <.0001). Participants from Africa (assessment 1 (AS1):ƙ =.487; AS2:0.491), Central/South America (AS1:ƙ =.513; AS2:0.511), and the Middle East (AS1:0.591; AS2:.599) achieved moderate reliability, while participants from North America (AS1:ƙ =.673; AS2:0.648) and Europe (AS1:ƙ =.682; AS2:0.681) achieved substantial reliability. Asian participants obtained substantial reliability on AS1 (ƙ =.632), but moderate reliability on AS2 (ƙ =.566). Although there was a large effect size, the low number of participants in certain regions did not provide adequate certainty that AO regions affected the likelihood of participants having excellent reproducibility (P =.342). Conclusions: The AO Spine Upper Cervical Injury Classification System can be applied with high accuracy, interobserver reliability, and intraobserver reproducibility. However, lower classification accuracy and reliability were found in regions of Africa and Central/South America, especially for severe atlas injuries (IIB and IIC) and atypical hangman’s type fractures (IIIB injuries). © The Author(s) 2022.