Background
In previous studies an association between deployment to Iraq or Afghanistan and an overall increased risk for post-traumatic stress disorder (PTSD) in UK armed forces has not been found. The lack of a deployment effect might be explained by including, in the comparison group, personnel deployed on other operations or who have experienced traumatic stressors unrelated to deployment.

Methods
The sample comprised 8261 regular UK armed forces personnel who deployed to Iraq, Afghanistan or other operational areas or were not deployed. Participants completed the PTSD CheckList – Civilian Version (PCL-C) and provided information about deployment history, demographic and service factors, serious accidents and childhood experiences.

Results
Deployment to Iraq or Afghanistan [odds ratio (OR) 1.2, 95% confidence interval (CI) 0.6–2.2] or elsewhere (OR 1.1, 95% CI 0.6–2.0) was unrelated to PTSD although holding a combat role was associated with PTSD if deployed to Iraq or Afghanistan (OR 2.7, 95% CI 1.9–3.9). Childhood adversity (OR 3.3, 95% CI 2.1–5.0), having left service (OR 2.7, 95% CI 1.9–4.0) and serious accident (OR 2.1, 95% CI 1.4–3.0) were associated with PTSD whereas higher rank was protective (OR 0.3, 95% CI 0.12–0.76).

Conclusions
For the majority of UK armed forces personnel, deployment whether to Iraq, Afghanistan or elsewhere confers no greater risk for PTSD than service in the armed forces per se but holding a combat role in those deployed to Iraq or Afghanistan is associated with PTSD. Vulnerability factors such as lower rank, childhood adversity and leaving service, and having had a serious accident, may be at least as important as holding a combat role in predicting PTSD in UK armed forces personnel.