AbstractBackgroundExposure to conflict, violence and forced displacement can increase poor mental health among affected populations. Our aim was to examine evidence on the burden of mental disorders and access to and effectiveness of mental health and psychosocial support (MHPSS) services in Syria and among Syrian refugees in neighboring countries.MethodsA systematic review was done following systematic review criteria. Twelve bibliographic databases and additional gray literature sources were searched for quantitative and qualitative studies. Descriptive analysis and quality assessment were conducted.ResultsTwenty-eight eligible studies were identified, of which two were with conflict-affected populations within Syria. Levels of post-traumatic stress disorder ranged from 16 to 84%, depression from 11 to 49%, and anxiety disorder from 49 to 55%. Common risk factors were exposures to trauma and having a personal or family history of mental disorder. Financial and socio-cultural barriers were identified as the main obstacles to accessing MHPSS care. Evaluations of MHPSS services, albeit from predominantly nonrandomised designs, reported positive treatment outcomes.ConclusionsThe MHPSS burden was high, but with considerable variation between studies. There are key evidence gaps on: MHPSS burden and interventions—particularly for those living within Syria; access and barriers to care; and implementation and evaluation of MHPSS interventions.