Ten patients suffering from post-traumatic stress disorder (PTSD) following a severe traumatic event, were assessed with event-related brain potentials (ERPs) in a modified oddball paradigm containing auditory standard, target, and novel tones. ERPs were assessed before and after a treatment session using the eye movement desensitization and reprocessing method. Compared to a control group that underwent sham treatment, ERPs of the patients showed a reduction of the P3a component in the post-treatment recording, suggesting a reduced orienting to novel stimuli and reduced arousal level after the treatment. Moreover, psychometric assessment revealed a marked improvement of the PTSD symptoms after treatment.