A meta-analysis was conducted to evaluate the comparative effectiveness of eye movement desensitization and reprocessing (EMDR) in the treatment of symptoms of over-arousal and comparing effectiveness in the treatment of anxiety and posttraumatic stress disorder (PTSD). Thirty-two effect sizes from randomized controlled trials were included in the analysis. Findings were mixed, indicating that EMDR was more effective than alternative viable treatments in the treatment of overarousal, but that true effect may range from 210% of a standard deviation favoring EMDR to 66% of a standard deviation favoring alternative viable treatments. No statistically significant differences for effectiveness were noted in the use of EMDR when treating anxiety versus trauma. Our findings indicate that on average, EMDR may be beneficial, but there is an equivalent chance that future applications with similar samples could result in findings regarded as considerably or categorically ineffective.