A better understanding of suicidal behavior is important to detect suicidality in at-risk populations such as patients with Borderline Personality Disorder (BPD), Posttraumatic Stress Disorder (PTSD) and Major Depressive Disorder (MDD). Suicidal tendencies are clinically assessed by verbal thoughts rather than specifically asking about mental images. This study examines whether imagery and verbal thoughts about suicide occur and differ between patients with BPD with and without comorbid PTSD compared to patients with MDD (clinical controls). All patient groups experienced suicide-related images. Patients with BPD with comorbid PTSD reported significantly more vivid images than patients with MDD. Severity of suicidal ideation, number of previous suicide attempts and childhood traumata were significantly associated with suicidal imagery across all patient groups. We demonstrate for the first time that suicide-related mental imagery occurs in BPD and is associated with suicidal ideation. This highlight the importance of assessing mental imagery-related to suicide in clinical practice.