Psychiatric patients who have shown suicidal behavior (SB) are belived to be at a particularly high risk of suicide. However, the number of studies that have sought ways to prevent suicide in this patient population is limited. The present study investigated the diagnosis and SB-related characteristics of psychiatric inpatients showing suicidal behavior prior to admission. One-hundred and fifty-seven eligible subjects were recruited from patients consecutively admitted to a large psychiatric facility during a 20-month period in 2006 and 2007,and underwent extensive research interviews. Percentages of diagnoses based on the Structured Clinical Interview for DSM-IV, Clinician Version (SCID-I, CV) in this series were: affective disorders, 62% ; anxiety disorders, 55% ; substance use disorders, 38% ; psychotic disorders, 27% ; and eating disorders, 10%. Eighty-seven percent of the subjects were diagnosed as having some type of personality disorder (PD) in the SCID-II interview. Borderline PD was diagnosed in 56% of the subjects,making it the most frequent type of PD in this series. Frequent SB in these subjects involved : self-cutting, 40% ; overdosing, 32% ; self-strangulation, 14% ; and jumping, 11%. Step-wise logistic regression analyses were conducted to examine the association of dichotomized SB-related clinical characteristics with diagnostic categories (affective disorders, psychotic disorders, substance use disorders, anxiety disorders, and cluster A,B and C PDs). The analyses demonstrated that three diagnostic categories were dominant in the association with clinical characteristics. Cluster B PD was associated with a history of overdosing, greater aggressiveness, interpersonal and life-situational life events, and childhood maltreatment (physical abuse and neglect). Anxiety disorders were related to histories of overdosing, dissociative symptoms in SB, excessive worry concerning life problems, and childhood neglect. Affective disorders were mainly associated with the characteristics of SB or SB-related symptoms : severe depressive symptoms and hopelessness,potentially fatal SB before admission such as self-strangulation, and dissociative symptoms in SB, though they did not show a significant relationship with pre-SB characteristics such as life events or childhood maltreatment. These findings will be helpful to develop treatment guidlines, SBprevention strategies, and future research regarding suicidal psychiatric patients.