BackgroundEarthquakes have caused profound physical and mental health impacts in human history. The Jiji earthquake, which had a magnitude of 7.6 on the Richter scale, occurred on 21 September 1999 in Taiwan. A close follow-up on the mental health status of affected adults after major natural disasters to construct the short-term and long-term risk and prevalence of stress-associated mental illnesses has not been performed by using the nationwide health databases. MethodsThis population-based cohort study included 468,804 adults affected by Jiji earthquake spanning from 2000 to 2019 who were matched at a 1:4 ratio with unaffected individuals based on age and sex (n = 1,875,216). Employing a subdistribution hazard regression analysis, we assessed the incidence of sleep, anxiety, and depressive disorders after Jiji earthquake. Corrections for multiple comparisons were carried out using the Benjamini–Hochberg procedure. ResultsAffected adults experienced an increased incidence of short-term (approximately twice) stress-associated psychiatric disorders. The risk of the post-traumatic stress disorder (PTSD) is significantly higher in the affected adults (40–64 years: aSHR: 92.0; ≥65 years: aSHR: 96.7, p < 0.0001). Middle-aged (aged 40–64 years) male adults presented with significantly more short-term (< one year) and long-term (up to 20 years) stress-related mental illnesses, i.e., insomnia, anxiety, and depressive disorders, than individuals in the control group. ConclusionsAn earthquake has significant short and long-term effects on sleep quality, anxiety, and depressive disorders in affected adults. Optimal short and long-term close monitoring is needed to deploy medical resources and socioeconomic support to relieve mental stress burdens.