On 12 March 2011 an earthquake devastated the Matsunoyama and Matsudai districts of Tokamachi City, Niigata, Japan. These areas had high pre-existing suicide rates, especially among the elderly. We investigated whether mental health status became worse among the sufferers 5 months after the earthquake, and what kind of factors were implicated in any changes. A 15-item questionnaire that tapped earthquake-related variables and the Kessler 10 Psychological Distress Scale to measure psychological distress were distributed to 1923 residents aged over 40 years. The mean age (S.D.) of the total 1731 respondents (male, 805; female, 926) was 68.2 (13.1) years. Of these, we assessed K10 scores from 1346 respondents. The mean scores (S.D.) for K10 and K6 (six selected items from the K10) were 5.8 (6.3) and 3.4 (3.9), respectively. Among the respondents, 9.1% and 3.2% obtained a score of K10 >= 15 and K6 >= 13, respectively. These scores showed slightly higher psychological distress, especially among the elderly, in comparison with existing community-based data. Categorical regression analysis revealed significant and relatively strong effects of initial psychological impact, decrease in sleep hours, advanced age, and decrease in interpersonal relationships within the community on the 1(10 score. The last item suggests the importance of socio-environmental factors in post-disaster mental health. (C) 2014 Elsevier Ireland Ltd. All rights reserved.