Background. Post-traumatic stress disorder (PTSD) typically involves a re- experiencing of traumatic events. In a previous P3 study it was found that PTSD patients react both selectively and involuntarily to combat-related pictures, exhibiting augmented P3 event-related potentials and thus providing a brain activity measure. The clinical application of these findings in differentiating PTSD patients from controls was tested. Method. Twenty Israeli combat veterans suffering from PTSD and 20 age-matched veterans without PTSD were evaluated. P3 potentials were recorded at Pz and Cz in response to visual motor-task target stimuli (pictures of domestic animals), non-target probe stimuli (combat-related pictures), and non-target irrelevant stimuli (pictures of furnishings and flowers). Results. Using the Fisher Linear Discrimination Method the P3 measures correctly classified 90% of the PTSD patients and 85% of the controls. Conclusions. Visual P3s recorded in response to combat-related pictorial stimuli may introduce an efficient tool for studying higher brain activity in PTSD, complementing other behavioral and psychophysiological measurements.