Abstract In Japan, there has not yet been a complete psychological autopsy study. The author conducted a retrospective study of failed suicides (quasi-completed suicides) admitted to an emergency critical care center. According to the lethality of suicide methods, 133 out of 265 subjects over 6 years (1986–1991) were classified as the absolutely dangerous (AD; the failed suicides) group. As a principal diagnosis, psychoses, endogenous depression, substance abuse were present in 75% of the AD group. The diagnostic distribution largely differed with depressive disorders being mainly in the older group (50+ years), and psychoses predominating in the younger group (<30 years). This study suggested that the majority of suicide victims in Japan also had mental disorders, and suicide prevention should be confronted with this clinical fact.