Neuroimaging studies of individuals with posttraumatic stress disorder (PTSD) have revealed altered patterns of activity in medial prefrontal brain regions, including the anterior cingulate cortex (ACC), an area implicated in affect regulation. Selective serotonin reuptake inhibitors (SSRIs) have been shown to effectively treat PTSD symptoms, but there remains a lack of functional neuroimaging research examining the effects of psychopharmacological treatment on brain function in PTSD. The purpose of this pilot study was to assess the effects of the SSRI paroxetine on neural responses to traumatic memories in a small sample of patients with PTSD, as measured with PET imaging; we hypothesized that paroxetine treatment would be associated with increased regional cerebral blood flow (rCBF) in the medial prefrontal cortex. Thirteen participants with PTSD were given controlled-release paroxetine (paroxetine CR) or placebo in a randomized, double-blind fashion for 12 weeks. Participants underwent brain imaging using positron emission tomography (PET) before and at the end of treatment in conjunction with exposure to neutral scripts and personalized trauma scripts. Participants treated with paroxetine CR and placebo both exhibited significantly increased rCBF in the ACC during trauma versus neutral script presentations; however, we noted an increase in function in the orbitofrontal cortex (OFC) in paroxetine-treated (but not placebo-treated) participants. Participants in both groups showed decreases in overall PTSD symptomatology following treatment; paroxetine-treated participants showed a slightly greater percentage decrease in symptoms. These preliminary findings indicate that increased ACC function represents a nonspecific response to treatment, whereas increased OFC function is specifically associated with paroxetine treatment in PTSD. These pilot data reveal putative mechanisms for SSRI treatment in PTSD and substantiate the need for large-scale placebo-controlled studies investigating these effects.