Substantial evidence supports association between childhood maltreatment and suicidal behaviour, however, a limited number of studies have examined psychological mechanisms mediating the relationship among patients with mood disorders.

To investigate directly the potential intermediating mechanisms between childhood maltreatment and suicidal behaviour among patients with mood disorders.

We examine by formal mediation analyses, if:

– the effect of childhood maltreatment on suicidal behaviour is mediated through borderline personality disorder traits;

– the mediation effect differs between lifetime suicidal ideation and lifetime suicide attempts.

Depressive disorder and bipolar disorder (ICD-10-DCR) patients (n = 287) from the Helsinki university psychiatric consortium (HUPC) Study were surveyed on self-reported childhood experiences, current depressive symptoms, borderline personality disorder traits and lifetime suicidal behaviour. Psychiatric records served to complement the information on suicide attempts.

The influence of childhood maltreatment on lifetime suicidal ideation and lifetime suicide attempts showed comparable total effects. In formal mediation analyses, borderline personality disorder traits mediated all of the total effect of childhood maltreatment on lifetime suicide attempts, but only 21% of the total effect on lifetime suicide ideation. The mediation effect was stronger for lifetime suicide attempts compared to ideation (P = 0.002) and independent of current depressive symptoms.

The mechanisms of the effect of childhood maltreatment on suicidal ideation and attempts may diverge among psychiatric patients with mood disorders. Borderline personality disorder traits may contribute to these mechanisms, although the influence appears considerably stronger for suicide attempts than for suicide ideation.

The authors have not supplied their declaration of competing interest.