This study examined mental health of victims in Hokkaido Nansei-oki Earthquake of 1993. The 28-item General Health Questionnaire (GHQ28) was administered to residents of the Aonae district of Okushiri Island, which was most heavily damaged by the earthquake. The accepted threshold for GHQ28 to indicate a risk for nonpsychotic psychiatric disorders is a score of six, and an extremely large proportion of the respondents exceeded the threshold. At ten months after the earthquake, 76.6% of respondents scored above 6, which only slightly dropped to 68.0% at 27 months. The results indicated that disaster victims' mental health was at risk for a long time and not just immediately after the disaster. Risk factors for GHQ28 scores at 27 months after the earthquake were analyzed, and relative risk ratios computed. The ratio was highest among people unable to return to employment or household work, 3.76 times more likely to exceed the threshold than others. A second risk factor, the severity of damage caused by the earthquake had a ratio of 3.61 for severe over minor damage. A ratio of 2.58 was found for people unable to talk or consult with someone else, and a 2.27 for those older than 50. Finally, the need to develop a practical system of psychological and social support, matched to the circumstances of individual victims, was discussed. Methodological suggestions were also made to improve future research.

Key words: natural disaster, mental health, GHQ28, research methodology