Posttraumatic stress disorder (PTSD) is a major public health problem in this country. It is estimated that at least one out of every seven women in our society have been the victim of childhood sexual abuse at least once before their 18th birthday. Previous studies have shown that stress is associated with damage to neurons of the hippocampus, a brain area involved in learning and memory. Also, imaging studies of brain function are consistent with dysfunction of the medial prefrontal cortex during presentation of traumatic cues. We have previously shown that serotonin reuptake inhibitor medications (paroxetine; Paxil) can change memory function and hippocampal structure in PTSD. We now propose to perform a placebo controlled study with Paxil CR (paroxetine hydrochloride controlled-release tablets), which is thought as paroxetine with less side-effects. The main purpose of this study is to determine the effects of Paxil CR on memory deficits measured with neuropsychological testing, hippocampal volume measured with a magnetic resonance imaging (MRI), medial prefrontal lobe cortical function estimated with PET, and cortisol response (reflecting the intensity of stress) in men and women with PTSD. We plan to recruit 40 subjects. After completing physical examination and evaluating neuropsychiatric history, patients will undergo an initial group of tests which includes memory testing, MRI and PET brain scan, and measurement of cortisol in their saliva. Afterwards, half will receive Paxil CR 12.5 to 62.5 mg and half will receive a placebo (sugar pill) in the beginning of the first 12 weeks as "Double Blind Phase". After 12 weeks, they will be administered memory tests, PET and MRI scan for the post-treatment phase. After this period, Paxil CR will be offered to the placebo group and followed for an additional 12 weeks. They will have final memory tests, and a MRI scan. We hypothesize that Paxil CR exerts its efficacy by acting on abnormal neural circuits, including hippocampus and prefrontal cortex, in PTSD.