Objective: To provide a better understanding of any associations between Disarmament, Demobilization, and Reintegration, previous head injury, and mental health symptoms among former combatants in Liberia. Methods: A cluster-sampled national survey of the adult household-based Liberian population. Findings: Former combatants with reported head injury were more likely to experience major depressive disorder symptoms, suicidal ideation and attempts, and current substance abuse. Former combatants with head injury are 2.83 times more likely to have major depressive disorder symptoms, and those with suspected traumatic brain injury are five times more likely to have post-traumatic stress disorder. Interpretation: The poor mental health of former combatants in Liberia, both child and adult, might be mitigated if Disarmament, Demobilization, and Reintegration programming assessed participants for head trauma and traumatic brain injury using simple screening methods. The specific health and mental health needs of ex-combatants-a highly vulnerable group-will need to be addressed by Liberia. If left untreated, ex-combatants with high rates of suicidal ideation and post-traumatic stress disorder might be susceptible to re-recruitment into new conflicts in the region.