This is a systematic controlled study examining the use of augmentation with pharmaotherapy for PTSD patients remaining symptomatic despite CBT (exposure therapy). The aims of the study include examination of: (1) the efficacy of paroxetine-CR compared to placebo as additions to ongoing exposure therapy in patients who failed to respond to brief, intensive CBT; (2) the tolerability of paroxetine-CR compared to placebo as additions to ongoing exposure therapy in patients who failed to respond to brief, intensive CBT; (3) the outcome of patients at 6 months follow-up to randomized treatment. Patients will initially have intensive (8 sessions over 4 weeks) prolonged exposure therapy. Patients who remain symptomatic will be randomzied to receive either flexibly-dosed paroxetine-CR (12.5 mg/d - 62.5 mg/d) or placebo in conjunction with additional 5 sessions of prolonged exposure over 10 weeks.