PURPOSE: In response to earlier reports that raised concerns about the tolerability of fluoxetine in the treatment of posttraumatic stress disorder (PTSD), this study was conducted to systematically delineate treatment-emergent symptoms (TES) associated with fluoxetine treatment of PTSD. METHODS: Sixty-five patients with PTSD enrolled in one of two identical-protocol, 12-week studies and received double-blind fluoxetine or placebo. TES data were obtained using a patient-rated checklist, Severity of Symptoms Scale (SOSS). RESULTS: Only a single patient discontinued treatment due to medication side effects. Compared to placebo, only three statistically significant TES (nausea, diarrhea, and thirst) occurred more frequently in fluoxetine subjects. Fluoxetine was not associated with any statistically significant activating effects. There were no statistically significant associations between the total number of TES experienced and treatment, gender, or comorbid depressive or panic disorders. CONCLUSIONS: This systematic assessment of TES indicated that PTSD patients tolerated fluoxetine well without pronounced activating side effects.