Post-traumatic stress disorder is a common, chronic, and often disabling mental illness. Selective serotonin reuptake inhibitors are the usual first-line treatment for post-traumatic stress disorder, but many patients fail to respond adequately. Thus, other treatment options, including the atypical antipsychotics such as risperidone, need to be tested. Women between the ages of 19 and 64 years with post-traumatic stress disorder were enrolled. Symptom severity was rated at baseline using the Treatment Outcomes Post-traumatic Stress Disorder Scale-8, Hamilton Rating Scale for Anxiety, Hamilton Rating Scale for Depression, and Clinician Administered Post-traumatic Stress Disorder Scale. After washout from other psychotropic medications, 20 participants were randomized to either risperidone or placebo. Total score on the Treatment Outcomes Post-traumatic Stress Disorder Scale-8 served as the primary outcome measure. Repeated-measures analysis of variance was followed by Newman–Keuls tests. A significant main effect exists for visits using the Treatment Outcomes Post-traumatic Stress Disorder Scale-8 raw score. For the treatment group, the difference between baseline Treatment Outcomes Post-traumatic Stress Disorder Scale-8 scores and treatment visit scores was significant beginning at visit 6 and continued through visit 11. No significant difference observed between baseline and any treatment visit for the placebo group. The Clinician Administered Post-traumatic Stress Disorder Scale, Hamilton Rating Scale for Anxiety, and Hamilton Rating Scale for Depression data revealed a similar pattern. In this small pilot study, risperidone monotherapy was more effective than placebo in the treatment of post-traumatic stress disorder.