BACKGROUND: Since 2015, Europe has been facing an unprecedented arrival of refugees and migrants: more than one million people entered via land and sea routes. During their travels, refugees and migrants often face harsh conditions, forced detention, and violence in transit countries. However, there is a lack of epidemiological quantitative evidence on their experiences and the mental health problems they face during their displacement. We aimed to document the types of violence experienced by migrants and refugees during their journey and while settled in Greece, and to measure the prevalence of anxiety disorders and access to legal information and procedures. METHODS: We conducted a cross-sectional population-based quantitative survey combined with an explanatory qualitative study in eight sites (representing the range of settlements) in Greece during winter 2016/17. The survey consisted of a structured questionnaire on experience of violence and an interviewer-administered anxiety disorder screening tool (Refugee Health Screener). RESULTS: In total, 1293 refugees were included, of whom 728 were Syrians (41.3% females) of median age 18 years (interquartile range 7-30). Depending on the site, between 31% and 77.5% reported having experienced at least one violent event in Syria, 24.8-57.5% during the journey to Greece, and 5-8% in their Greek settlement. Over 75% (up to 92%) of respondents ≥15 years screened positive for anxiety disorder, which warranted referral for mental health evaluation, which was only accepted by 69-82% of participants. Access to legal information and assistance about asylum procedures were considered poor to non-existent for the majority, and the uncertainty of their status exacerbated their anxiety. CONCLUSIONS: This survey, conducted during a mass refugee crisis in a European Community country, provides important data on experiences in different refugee settings and reports the high levels of violence experienced by Syrian refugees during their journeys, the high prevalence of anxiety disorders, and the shortcomings of the international protective response.