Positive and negative symptoms of psychosis may be common in patients with chronic post-traumatic stress disorder (PTSD), but few studies have investigated the use of antipsychotic agents in these patients. This preliminary study examined the potential efficacy of risperidone in treating psychotic symptoms associated with chronic PTSD. In a 5-week, prospective, randomized, double-blind, placebo-controlled trial, adjunctive risperidone treatment was assessed in 40 combat veterans with chronic PTSD and comorbid psychotic features. Most patients were receiving antidepressants and some other psychotics with doses of concurrent medications held constant for at least 1 month prior to and during the study. Thirty-seven patients completed at least 1 week of treatment with risperidone or placebo. The Positive and Negative Syndrome Scale (PANSS) and the Clinician Administered PTSD Scale (CAPS) were used to assess symptoms. The PANSS was the primary outcome measure. At treatment endpoint, risperidone-treated patients showed a significantly greater decrease from baseline, albeit modest, in psychotic symptoms (PANSS total scores) than placebo-treated patients (P<0.05). CAPS ratings declined significantly in both groups but did not differ significantly between groups. However, CAPS re-experiencing subscale scores had greater improvement in the risperidone-treated patients at week 5 (P<0.05, completer analysis) with a trend towards greater improvement versus placebo a endpoint (P<0.1, LOCF). Risperidone was well tolerated with minimal extrapyramidal symptoms. These preliminary results support studying the potential efficacy of risperidone for treating global psychotic symptoms associated with chronic PTSD with a suggestion that core re-experiencing symptoms may also be responsive. Further research using randomized, controlled trial designs in larger patient groups are needed to define more adequately the role of risperidone and other atypical agents in PTSD.