Syria has been the main country of citizenship of refugees in Germany since 2013. Syrians face numerous human rights violations in their country that can be accompanied by the experience of potentially traumatic events, loss and displacement. Along the migration process, refugees are exposed to various factors that can have an impact on mental health. The aim of this study is to investigate sociodemographic, war- and flight-related as well as post-migration factors as predictors of posttraumatic stress, depression, somatization and anxiety in Syrian refugees with posttraumatic stress symptoms based in Germany. Data were based on the baseline sample of the "Sanadak" randomized-controlled trial. A total of 133 adult Syrian refugees participated in the study. A questionnaire covered sociodemographic and flight-related questions as well as standardized instruments for symptoms of PTSD (PDS-5), depression (PHQ-9), somatization (PHQ-15), anxiety (GAD-7), generalized self-efficacy (GSE), religiousness (Z-Scale), social support (ESSI) and mental health stigma (SSMIS-SF). Linear regression models were executed to predict mental health outcomes. Sociodemographic predictors (i.e., female sex, higher education) and flight-related predicting factors (i.e., variability of traumatic events) have a negative impact on mental health in Syrian refugees with posttraumatic stress symptoms in Germany. Mental health stigma predicts worse mental health outcomes. Post-migration factors have a major impact on mental health, such as low income, lack of social support, low life satisfaction or a strongly felt connection to Syria. Somatization is an important manifestation of mental distress in Syrian refugees with posttraumatic stress symptoms. Our study showed a range of factors predicting the mental health of Syrian refugees with posttraumatic stress symptoms. Measures to foster mental health could be securing financial security, promoting gender equality and tailored psychosocial programs addressing mental health stigma, loss and social support networks.