Aim: The present study was conducted to examine differences in psychosocial and psychiatric characteristics between suicide completers with and without a history of psychiatric treatment within the year before death, using a psychological autopsy method. Methods: A semi-structured interview was administered by a psychiatrist and other mental health professionals for the closest bereaved of 76 suicide completers. Results: Suicide completers with a history of psychiatric treatment (n = 38) were significantly younger than those without (n = 38) (P < 0.01), and a significantly higher proportion of cases in the treatment group were estimated to be suffering from schizophrenia. Further, in 57.9% of the treatment group, the fatal suicidal behavior involved overdose with prescribed psychotropic drugs. In addition, female suicide completers in the treatment group were more likely to have a history of self-harm or non-fatal suicidal behavior. Conclusion: Many suicide completers who received psychiatric treatment were young adults. It was common for suicide completers to overdose on prescribed drugs as a supplementary means of suicide, and many experienced self-harming behavior before death. In addition, a higher proportion of the treatment cases suffered from schizophrenia.