Syria is the main country of origin for refugees in the world. The prevalence of mental disorders in this population is high, but there is a lack of more comprehensive data on mental health issues in this population. This study aims to review the literature for mental health outcomes in Syrian refugees. We performed a systematic quantitative literature review of original observational studies indexed on the MEDLINE via PubMed, Embase, Web of Science, PsycINFO, LILACS, and SciELO databases with quantitative data reporting mental health outcomes in Syrian refugees. A descriptive analysis was conducted, and the quality of the included studies was assessed using an adaptation from The National Institutes of Health (NIH) quality assessment tool for observational studies. The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines were followed. A total of 64 studies were included. The majority were published between 2019 and 2020, and focused on the prevalence of post-traumatic stress disorder (PTSD), depression, and anxiety, with a wide range of variations. Other outcomes were difficulties in the post-migration period and promotive factors for mental health, such as resilience, positive coping strategies, and psychosocial well-being. High prevalence rates of mental disorders were observed, as well as risk factors for their occurrence. Studies showed a very high variability of prevalence rates and heterogeneity in methodologies. There is a need for research focusing on other determinants and specific necessities for mental health, especially in the post-resettlement period.