Exposure to childhood adversity may explain why only a minority of combatants exposed to trauma develop psychological problems.

To examine the association between self-reported childhood vulnerability and later health outcomes in a large randomly selected male military cohort.

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).

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.

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.

Deployment to the 2003 Iraq War was associated with ill health in reserve armed forces personnel.

To investigate reasons for the excess of ill health in reservists.

UK personnel who were deployed to the 2003 Iraq War completed a health survey about experiences on deployment to Iraq. Health status was measured using self-report of common mental disorders, post-traumatic stress disorder (PTSD), fatigue, physical symptoms and well-being.

Reservists were older and of higher rank than the regular forces. They reported higher exposure to traumatic experiences, lower unit cohesion, more problems adjusting to homecoming and lower marital satisfaction. Most health outcomes could be explained by role, experience of traumatic events or unit cohesion in theatre. PTSD symptoms were the one exception and were paradoxically most powerfully affected by differences in problems at home rather than events in Iraq.

The increased ill-health of reservists appears to be due to experiences on deployment and difficulties with homecoming.