Background: On March 11, 2011, the Great East Japan Earthquake and tsunami that followed caused severe damage along Japans northeastern coastline and to the Fukushima Daiichi nuclear power plant. To date, there are few reports specifically examining psychological distress in rescue workers in Japan. Moreover, it is unclear to what extent concern over radiation exposure has caused psychological distress to such workers deployed in the disaster area. Methods: One month after the disaster, 424 of 1816 (24%) disaster medical assistance team workers deployed to the disaster area were assessed. Concern over radiation exposure was evaluated by a single self-reported question. General psychological distress was assessed with the Kessler 6 scale (K6), depressive symptoms with the Center for Epidemiologic Studies Depression Scale (CES-D), fear and sense of helplessness with the Peritraumatic Distress Inventory (PDI), and posttraumatic stress symptoms with the Impact of Event Scale-Revised (IES-R). Results: Radiation exposure was a concern for 39 (9.2%) respondents. Concern over radiation exposure was significantly associated with higher scores on the K6, CES-D, PDI, and IES-R. After controlling for age, occupation, disaster operation experience, duration of time spent watching earthquake news, and past history of psychiatric illness, these associations remained significant in men, but did not remain significant in women for the CES-D and PDI scores. Conclusion: The findings suggest that concern over radiation exposure was strongly associated with psychological distress. Reliable, accurate information on radiation exposure might reduce deployment-related distress in disaster rescue workers.