Background Breakdowns in the ethical conduct of soldiers towards non-combatants on the battlefi eld are of grave concern in war. Evidence-based training approaches to prevent unethical conduct are scarce. We assessed the eff ectiveness of battlefi eld-ethics training and factors associated with unethical battlefi eld conduct. Methods The training package, based on movie vignettes and leader-led discussions, was administered 7 to 8 months into a 15-month high-intensity combat deployment in Iraq, between Dec 11, 2007, and Jan 30, 2008. Soldiers from an infantry brigade combat team (total population about 3500) were randomly selected, on the basis of company and the last four digits of each soldier’s social security number, and invited to comp...