The purpose of this study was to evaluate an animal model of posttraumatic stress disorder (PTSD) in mice. The model featured repeated exposures to situational reminders of a traumatic stress, which consisted of a brief electric shock, and included assessment of two behavioral parameters and the startle reflex. The findings indicated an initial, but unsustained, increase in locomotor activity in a neutral environment due to traumatic stress. Exposure to situational reminders was associated with a persistent bidirectional abnormal behavioral pattern in a fear-provoking environment and a progressive increase over time in the magnitude of the startle reflex. Exposure to situational reminders also produced an increase in aggressive behavior. This animal model appears to produce behavioral changes analogous to those seen in patients with PTSD.