Humanitarian relief work is a growing field characterized by ongoing exposure to primary and secondary trauma, which has implications for workers' occupational mental health. This paper reviews and summarizes research to date on mental health effects of relief work. Twelve studies on relief workers and 5 studies on organizations that employ relief workers are examined to determine whether relief work is a risk factor for trauma-related mental illness. Although studies are inconsistent regarding methods and outcomes documenting trauma-related mental illness among relief workers, it appears that relief workers, compared with the general population, experience elevated trauma rates and suffer from more posttraumatic stress disorder, depression, and anxiety. Organizations that employ relief workers have varying approaches to train for these risks, and more support in the field is needed.