Health Evidence Network Synthesis Report, No. 47 The increasing number of refugees, asylum seekers and irregular migrants poses a challenge for mental health services in Europe. This review found that these groups are exposed to risk factors for mental disorders before, during and after migration. The prevalence rates of psychotic, mood and substance use disorders in these groups are variable but overall are similar to those in the host populations; however, the rates of post-traumatic stress disorder in refugees and asylum seekers are higher.