Objective This study examined the diagnostic validity of a three-item ultra-brief screening tool for online gaming disorder in line with the gaming disorder criteria in the International Classification of Diseases 11th Revision. Methods The Three-item Gaming disorder Test-Online-Centered (TIGTOC) was composed of three items using a four-point Likert scale selected from the Internet Game Use-Elicited Symptom Screen (IGUESS). Among a cohort of 2319 young-adolescent Internet users, the baseline data of 228 healthy controls and 45 Internet-gaming-disorder cases were analyzed. Receiver operation characteristic (ROC) analysis was performed using mental health specialists’ diagnoses as the gold standard. Results The ROC curve analysis showed an area under the curve of 86%. Using a cut-off score of 4 from a full range of 0-9, the sensitivity, specificity, and Cronbach’s α were 72%, 90%, and 0.811, respectively. TIGTOC scores was positively associated with time spent on online gaming, depressive symptoms, attention-deficit/hyperactivity disorder symptoms, and addictive Internet use. Conclusion The TIGTOC appears to be a brief, valid, and reliable screening tool for online gaming disorder within the community or in primary care settings.