Soldiers preoccupied with threat at the time of enlistment or with avoiding it just before deployment were more likely to develop post-traumatic stress disorder (PTSD), in a study of Israeli infantrymen. Such pre-deployment threat vigilance and avoidance, interacting with combat experience and an emotion-related gene, accounted for more than a third of PTSD symptoms that emerged later. Computerized training that helps modify such attention biases might help protect soldiers from the disorder.