The investigators propose to study the clinical, neuropsychological, and neuroendocrine effects of short-term treatment with one dose of mifepristone (600 mg/day) in a well-characterized sample of Veterans with PTSD to determine if this treatment is effective in achieving a clinical response in PTSD, as well as improving clinical symptoms and quality of life. Furthermore, if pulse therapy with mifepristone has sustained effects, it holds out the promise of a very different approach to pharmacological treatment, one that may be preferable to Veterans who do not want to be on psychopharmacological treatments continuously or long-term.