In June 2001, we assessed mental health problems among Karenni refugees residing in camps in Mae Hong Son, Thailand, to determine the prevalence of mental illness, identify risk factors, and develop a culturally appropriate intervention program. A systematic random sample was used with stratification for the three camps; 495 people aged 15 years or older from 317 households participated. We constructed a questionnaire that included demographic characteristics, culture-specific symptoms of mental illness, the Hopkins Symptoms Checklist-25, the Harvard Trauma Questionnaire, and selected questions from the SF-36 Health Survey. Mental health outcome scores indicated elevated levels of depression and anxiety symptoms; post-traumatic stress disorder (PTSD) scores were comparable to scores in other communities affected by war and persecution. Psychosocial risk factors for poorer mental health and social functioning outcomes were insufficient food, higher number of trauma events, previous mental illness, and landmine injuries. Modifications in refugee policy may improve social functioning, and innovative mental health and psychosocial programs need to be implemented, monitored, and evaluated for efficacy.