AIMS: Syrian refugees may have increased mental health needs due to the frequent exposure to potentially traumatic events and violence experienced during the flight from their home country, breakdown of supportive social networks and daily life stressors related to refugee life. The aim of this study is to report evidence on mental health needs and access to mental health and psychosocial support (MHPSS) among Syrians refugees living in Sultanbeyli-Istanbul, Turkey. METHODS: A cross-sectional survey was conducted among Syrian refugees aged 18 years or over in Sultanbeyli between February and May 2018. We used random sampling to select respondents by using the registration system of the municipality. Data among 1678 Syrian refugees were collected on mental health outcomes using the Posttraumatic Stress Disorder (PTSD) Checklist (PCL-5) and the Hopkins Symptoms Checklist (HSCL-25) for depression and anxiety. We also collected data on health care utilisation, barriers to seeking and continuing care as well as knowledge and attitudes towards mental health. Descriptive analyses were used. RESULTS: The estimated prevalence of symptoms of PTSD, depression and anxiety was 19.6, 34.7 and 36.1%, respectively. In total, 249 respondents (15%) screened positive for either PTSD, depression or anxiety in our survey and self-reported emotional/behavioural problems since arriving in Sultanbeyli. The treatment gap (the proportion of these 249 people who did not seek care) was 89% for PTSD, 90% for anxiety and 88% for depression. Several structural and attitudinal barriers for not seeking care were reported, including the cost of mental health care, the belief that time would improve symptoms, fear of being stigmatised and lack of knowledge on where and how to get help. Some negative attitudes towards people with mental health problems were reported by respondents. CONCLUSIONS: Syrian refugees hardly access MHPSS services despite high mental health needs, and despite formally having access to the public mental health system in Turkey. To overcome the treatment gap, MHPSS programmes need to be implemented in the community and need to overcome the barriers to seeking care which were identified in this study. Mental health awareness raising activities should be provided in the community alongside the delivery of psychological interventions. This is to increase help-seeking and to tackle negative attitudes towards mental health and people with mental health problems.