Objectives. The objective of this study is to evaluate the relationship between suicidal ideation (SI), structural brain damage, and cognitive deficits in patients with penetrating traumatic brain injury (pTBI).Methods. Vietnam War veterans (n = 142) with pTBI to the prefrontal cortex (PFC) underwent combination of neuropsychological and psychiatric examinations and non-contrast CT brain scan. Patients were divided into SI positive (SI+) and SI negative (SI-) groups according to the SI item of the Beck Depression Inventory.Results. Lesions to the left rostrolateral PFC (rlPFC) were associated with a lower risk of SI independent of depression and global functioning. Left rlPFC lesion also reduced abstract reasoning skills, which mediated the lesion effects on suicide ideation.Conclusions. The left rlPFC plays a crucial role in SI independently of depression and global functioning. © Cambridge University Press 2019.