IntroductionIt is well-known that suicide and excess mortality are high in patients with psychiatric illnesses and this has long been an important issue in the field of mental health. We aim to investigate suicide and other-cause deaths in patients with psychiatric illnesses. MethodsThis retrospective, population-based cohort was based on the National Health Insurance claims data of the first admission with a principal diagnosis of major psychiatric disorder between 2010 and 2011, and followed up to 2020. A total of 95,855 participants were enrolled. Suicide and other-cause mortality were assessed through Log-rank test and Kaplan-Meier curve. ResultsThere were 95,855 patients, with an average age of 48.2 years. The number of suicide deaths and other-cause deaths was 2408 (288.1 per 100,000 person-years) and 15,192 (1817.6 per 100,000 person-years), respectively. The rate of healthcare utilization prior to suicide was 95.0 %, and the rate of utilization prior to one week before suicide was 43.5 %. The risk of suicide was highest in patients with depression, followed by alcohol use disorder, schizophrenia, and bipolar disorder. ConclusionsThis study revealed various factors related to healthcare utilization associated with suicide and other-cause deaths in psychiatric patients. Educating frontline healthcare professionals, psychiatrists, emergency department personnel, and general practice doctors using such as Gatekeeper program is important to prevent suicides.