Arq Centrum 45 is a TOPGGz-certified mental health institution for people with psychological complaints after violence. Undocumented migrants is one of the specific target populations for treatment, expertise development and scientific research. For people within the region of Amsterdam with post-traumatic stress disorder we offer treatment. For patients within of outside this region we offer diagnosis and advice after referral of a general practitioner. For colleagues working in mental healthcare we offer second opinion. Centrum 45 is part of Arq Psychotrauma Expert Group. Arq is also involved in policy advice concerning undocumented migrants.