Electroconvulsive therapy (ECT) has been successfully used in the treatment of depression, particularly when the illness is refractory to pharmacological therapy. A recent study has shown that ECT is also effective in reducing both depressive and posttraumatic stress disorder (PTSD) symptoms in patients with major depression (MDD) and co-occurring PTSD. This raises the possibility that ECT might be effective in the treatment of PTSD, a disease whose prevalence has increased substantially in recent years. A characteristic symptom of PTSD is an exaggerated reactivity to startling sounds (acoustic startle response; ASR). In the present study, we investigated the effects of electroconvulsive shocks (ECS) on the ASR, in a rat model of traumatic stress. The animals were subjected to a restraint/tailshock paradigm and then administered ECS. ASR measurements were obtained at several time points following ECS administration. Although ECS had no effect in control rats, it significantly exacerbated the already potentiated ASR in the stressed group. While ECT may prove to be an effective treatment for certain symptoms of co-occurring MDD/PTSD or PTSD alone, it may exacerbate heightened arousal associated with PTSD.