More than 29 armed conflicts involving 25 countries are now occurring around the globe.1 For people in the United Kingdom and United States the situation in Iraq and Afghanistan is a constant reminder of the cost of war. The price that soldiers, sailors, airmen, marines, and their families pay is always considerable.

In this week's BMJ, Rona and colleagues assess the effect of the frequency and duration of deployment on the mental health of 5547 randomly chosen military personnel with experience in deployment.2 They found that people who were deployed for more than 12 months in the past three years were more likely to have mental health problems (odds ratio for post-traumatic stress disorder 1.55, 95% confidence interval 1.07 to 2.32), although exposure to combat partly accounted for these associations. Post-traumatic stress disorder was more likely when a mismatch occurred between the expected and actual lengths of deployment.

The study could help identify those at high risk of long term disability and guide policy.3 Deployment is a strange term. Few people would suggest that deployment …