The aim of the present study was to survey a cohort population for the risk factors of post-traumatic stress disorder (PTSD) and major depression, and the prevalence of different psychiatric disorders at 6 months and 2 and 3 years after a major earthquake. The Disaster-Related Psychological Screening Test (DRPST), part I, and the Mini-International Neuropsychiatric Interview (MINI) were, respectively, administered by trained interviewers and psychiatrists in this community-interview program. The prevalence of PTSD decreased from 8.3% at 6 months to 4.2% at 3 years after the earthquake. Suicidality increased from 4.2% at 6 months and 5.6% at 2 years to 6.0% at 3 years after the earthquake; drug abuse/dependence increased from 2.3% at 6 months to 5.1% at 3 years after the disaster. The risk factors for PTSD and major depression in various post-disaster stages were determined. Earthquake survivors had a high percentage of psychiatric disorders in the first 2 years, and then the prevalence declined. Following the devastation caused by the Chi-Chi earthquake, it is important to focus on treating symptoms of major depression and PTSD and eliminating the risk factors for both of these disorders in survivors to avoid the increase in suicidality.