This is a single-blind, placebo-controlled, parallel group study to evaluate the efficacy of BRL29060A (paroxetine hydrochloride hydrate, hereafter paroxetine) administered orally over the dose range of 20 mg to 50 mg once daily after supper for 12 weeks in Japanese patients with posttraumatic stress disorder (PTSD) as assessed by the change from baseline in CAPS-SX total score. Also the effect of paroxetine on regional cerebral blood flow (rCBF) induced by subthreshold emotional arousing (or symptom stimulating) tasks will be determined using functional magnetic resonance imaging (fMRI) for exploratory assessment of the correlation between the change in rCBF and the efficacy.