Recently, studies of pharmacotherapy for post-traumatic stress disorder (PTSD) have been focused on serotonin-selective reuptake inhibitors (SSRI), despite a number of treatment-limiting side-effects. Mirtazapine, a novel drug with both noradrenergic and serotonergic properties, may be effective in individuals who demonstrate intolerance to side-effects of and a limited response to SSRIs. Six outpatients with severe, chronic PTSD were treated with mirtazapine, up to 45 mg/day for 8 weeks. Efficacy assessments and side-effect monitoring were performed at baseline and weeks 2, 4, 6 and 8. Fifty percent of the sample demonstrated improvement of 50% or more from baseline using a global rating. In addition, improvements were noted on both interviewer-administered and self-rated scales of PTSD and of depression. The drug was well tolerated with few significant side-effects. Mirtazapine was associated with clinical improvement in 50% of subjects with severe, chronic PTSD, suggesting a need for further investigation in double-blind, placebo-controlled trials.