Background: Since the outbreak of the Syrian war in 2011, close to 6 million Syrian refugees have escaped to Syria’s neighbouring countries, including Lebanon. Evidence suggests rising levels of mental health disorders among Syrian refugee populations. Yet, to the best of our knowledge, large-scale studies addressing the mental health of adult Syrian refugees in Lebanon are lacking. Aims: We examined the prevalence of depression symptoms, which represent a common and debilitating mental health disorder among Syrian refugee populations in Lebanon, along with their sociodemographic and clinical correlates.Methods: A cross-sectional survey design was conducted as part of a collaborative project-“Sijilli”- led by the Global Health Institute at the American University of Beirut (Beirut, Lebanon) across 4 informal tented settlements for refugees (Beirut, Bekaa, North, South) in Lebanon among adult Syrian refugees (≥18), over a period extending from 2018 to 2020. The survey inquired about participants’ sociodemographic and clinical characteristics, and screened participants for symptoms of depression through sequential methodology using the Patient Health Questionnaire (PHQ-2 and PHQ-9). Results: A total of 3255 adult Syrian refugees were enrolled in the study. Of those refugees, only 51.6% (n=1678) screened positive on the PHQ-2 and were therefore eligible to complete the PHQ-9. The PHQ-9 analysis revealed high prevalence (25%) of moderate to severe depression in the total sample, suggestive of high probability for major depression disorder (MDD). Further analyses indicate that being ≥45 years of age (OR 1.70, 95% CI 1.22-2.36), a woman (OR 1.35, 95% CI 1.07-1.69), divorced/separated (OR 3.32, 95% CI 1.57-7.01), reporting a neurological (OR 1.77, 95% CI 1.20-2.61) or a mental health condition (OR 5.30, 95% CI 2.40-11.66) are major risk factors for MDD.Conclusion: Our study suggests that one in four Syrian refugees in Lebanon have probable MDD, and our findings have important public health and clinical implications on refugee health. There is a need to enhance screening efforts, to improve access and referral to mental health services, and to improve post-migration factors among Syrian refugees in Lebanon.