Governments around the world use immigration detention to detain and deport irregular immigrants, which negatively affects their health. The aim of this thesis was to explore, describe and identify factors that could mitigate the effect of immigration detention on the health of detainees. This was a mixed method study using qualitative methods (Papers I and II), quantitative methods (Paper III) and descriptive case comparison (Paper IV) comparing the Swedish system to the system in the Benelux countries (Belgium, the Netherlands and Luxembourg). The study design was strengthened by triangulation of methods and data sources. Detainees experienced lack of control over their own lives due to lack of information in a language they can understand, inadequate responses from detention staff and restrictions within detention centers further limiting their liberty. Duration of detention was negatively associated with satisfaction of services provided in detention and the detainees’ Quality of Life (QOL). Detainees had low QOL domain scores with the psychological domain having the lowest score (41.9/100). The most significant factor positively associated with the QOL of detainees was the support received from detention staff. A sense of fear was present among detainees and staff. Detainees’ fear was due to their inadequate interaction with authorities, perceiving it as threatening, and due to their worry of facing repercussions of being involved in incidents caused by others. The potential for physical threat from detainees created a sense of fear among the staff. The detention staff expressed the need for more support to manage their emotional dilemma and role conflict of being a civil servant, simultaneously enabling the deportation process while providing humane care to detainees as fellow human beings. Detention centers in the Benelux countries had more categories of staff providing different services to detainees. Compared to the Benelux countries, healthcare services at the Swedish detention centers were limited. ...