Background: The ICD-11 classifies posttraumatic stress disorder (PTSD) and complex PTSD (CPTSD) as two distinct diagnoses. Few studies have tested the validity of ICD-11 CPTSD in non-Western settings, particularly in Asia. Objective: This study assessed the factorial, concurrent, and discriminant validity of CPTSD symptoms with four samples of young adults from mainland China, Hong Kong, Japan, and Taiwan. Method: Young adults aged 18–24 years were recruited by convenience sampling and provided their data anonymously online. Study measures included the International Trauma Questionnaire (ITQ) to measure PTSD and CPTSD, and measures of childhood adversity, depression, anxiety, age, and sex. Confirmatory factor analysis (CFA) was performed for each sample to evaluate the validity of two CPTSD measurement models. Structural equation modelling (SEM) was used to determine the multivariate associations between study variables for the full sample. Results: A total of 1,346 young adults completed the survey. CFA showed both models of CPTSD examined fit the data well across all four samples. SEM findings showed that number of childhood adversities significantly associated with both PTSD and CPTSD factors; depression significantly associated with CPTSD factors but not PTSD, whereas anxiety significantly associated with both. Conclusions: Study findings provide evidence for PTSD and CPTSD as separate and valid diagnoses in Asia. More cross-cultural comparisons are needed to understand whether risks for either condition differ by geographical or sociocultural norms.