Objective: Suicide is the leading cause of death in 10-39-year-olds in South Korea, and the second highest rate among the OECD countries. However, few studies have investigated the particularity of completed suicide in South Korea. Methods: Study subjects consisted of 2,838 suicide cases and 56,758 age and sex matched living controls from a national representative sample of 1,025,340 South Koreans. They were obtained from the Korean National Health Insurance Service-National Sample Cohort (NHIS-NSC) with follow-up up to 12 years. We obtained information on primary diagnosis of any ICD-10 disorder along with suicide cases during their lifetime. Results: Among ICD-10 disorders, depression was the most common disorder (19.10%, n=542), found in victims of completed suicides except for common medical disorders such as hypertensive crisis, respiratory tract infection or arthropathies. After adjusting for sex, age, economic status, disability, and disorders, schizophrenia showed the strongest association with suicide (AOR: 28.56, 95% CI: 19.58-41.66) among all ICD-10 disorders, followed by psoriasis, multiple body injury, epilepsy, sleep disorder, depression, and bipolar disorder. For age groups, ≤19 years was associated with anxiety disorder (AOR=80.65, 95% CI: 13.33-487.93), 20-34 years with epilepsy (AOR=134.92, 95% CI: 33.69–540.37), both 35–49 years (AOR=108.57, 95% CI: 37.17;317.09) and 50–65 years (AOR=189.41 95% CI: 26.59–1349.31), with schizophrenia, and >65 years (AOR=44.7, 95% CI: 8.93–223.63) with psoriasis. Conclusion: Psychiatric and physical disorders carried greatly increased risks and numbers of suicides in South Korea. Schizophrenia was the strongest risk factor, especially 35–65 years, and depression was the most common in suicide victims among ICD-10 disorders in South Korea.