A growing body of data indicates that patients with posttraumatic stress disorder (PTSD) have regionally selective alterations in brain metabolism and processing of information. For example, neuroimaging studies reveal increased blood flow and glucose utilization in right frontal, limbic and paralimibic brain structures in patients with PTSD, particularly when they are recalling the traumatic event associated with their symptoms. These alterations in regional brain activity are thought to be related, in part, to the distressing emotional symptoms associated with traumatic memories. Autonomic Nervous System (ANS) dysregulation is common in PTSD, with sympathetic hyper-reactivity and relative lack of parasympathetic modulation. In addition, abnormalities in hormone levels such as thyroid hormones and the hypothalmic-pituitary-adrenal axis have been demonstrated. Repetitive transcranial magnetic stimulation may provide a non-invasive technique for normalizing the alterations in regional brain metabolism, possibly leading to improvements in PTSD symptoms and concomitant improvement in ANS and hormonal balance. In particular, preliminary clinical data indicate that low frequency (i.e., approximately 0.9-1 Hz) rTMS stimulation leads to a decrease in regional cerebral blood flow. The purpose of the present study is to determine, using a placebo-controlled, parallel design, whether right frontal rTMS stimulation in patients with posttraumatic stress disorder leads to symptomatic improvement, reductions in hemispheric regional blood flow, and improvements in ANS regulation. The study hypothesis is that 1 Hz right frontal rTMS stimulation will be superior to sham stimulation in reducing PTSD symptoms and physiology including improving abnormalities in regional cerebral blood flow, vagal tone, and circulating hormone levels.