BACKGROUND: Exposure to childhood adversity may explain why only a minority of combatants exposed to trauma develop psychological problems. AIMS: To examine the association between self-reported childhood vulnerability and later health outcomes in a large randomly selected male military cohort. METHOD: Data are derived from the first stage of a cohort study comparing Iraq veterans and non-deployed UK military personnel. We describe data collected by questionnaire from males in the regular UK armed forces (n=7937). RESULTS: Pre-enlistment vulnerability is associated with being single, of lower rank, having low educational attainment and serving in the Army. Pre-enlistment vulnerability is associated with a variety of negative health outcomes. Two main factors emerge as important predictors of ill health: a 'family relationships' factor reflecting the home environment and an 'externalising behaviour' factor reflecting behavioural disturbance. CONCLUSIONS: Pre-enlistment vulnerability is an important individual risk factor for ill health in military men. Awareness of such factors is important in understanding post-combat psychiatric disorder.