RESEARCH ARTICLE A Case Series Investigating Acceptance and Commitment Therapy as a Treatment for Previously Treated, Unremitted Patients with Anorexia Nervosa M. I. Berman 1 * , K. N. Boutelle 2 & S. J. Crow 3 1 Dartmouth Medical School, NH, USA 2 University of California, San Diego, CA, USA 3 University of Minnesota, Twin Cities, MN, USA Abstract The aim of the present study was to evaluate the effectiveness of Acceptance and Commitment Therapy (ACT) for treatment of anorexia nervosa (AN) using a case series methodology among participants with a history of prior treatment for AN. Three participants enrolled; all completed the study. All participants had a history of 1–20 years of intensive eating disorder treatment prior to enrollment. Participants were seen for 17–19 twice-weekly sessions of manualized ACT. Symptoms were assessed at baseline, post-treatment and 1-year follow-up. All participants experienced clinically significant improvement on at least some measures; no participants worsened or lost weight even at 1-year follow-up. Simulation modelling analysis (SMA) revealed for some participants an increase in weight gain and a decrease in eating disorder symptoms during the treatment phase as compared to a baseline assessment phase. These data, although preliminary, suggest that ACT could be a promising treatment for subthreshold or clinical cases of AN, even with chronic participants or those with medical complications. Copyright # 2009 John Wiley & Sons, Ltd and Eating Disorders Association. Keywords anorexia nervosa; Acceptance and Commitment Therapy; simulation modelling analysis; eating disorder treatment *Correspondence M. I. Berman, PhD, Department of Psychiatry, Dartmouth Medical School, Dartmouth Hitchcock Medical Center, 1 Medical Center Drive, Lebanon, NH 03756-0001, USA. Tel: 603-650-7520, Fax: 603-650-5842. Email: Margit.I.Berman@dartmouth.edu Published online 16 September 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/erv.962 Introduction There is a pressing need for treatment development research in anorexia nervosa (AN). AN is a serious disorder, with high mortality rates from suicide as well as medical complications. To date, there are no known efficacious treatments, medical or psychological, for AN (Agras et al., 2004). Few efficacy trials of psychological treatments for AN have been published, and the methodological quality of published trials is generally relatively poor (Agras et al.). Treatment development research in AN has been so challenging that some researchers have suggested that Randomized Controlled Trial (RCT) methodologies should be temporarily abandoned in this area until more preliminary treatment development research has identified new, promising treatments (Fairburn, 2005). AN thus represents a case where there is enormous clinical need for effective treatments, but strong reason to supplement efficacy research in the area with method- ologies that evaluate the process and therapeutic effectiveness of psychotherapies used in the field. 426 Eur. Eat. Disorders Rev. 17 (2009) 426–434 ß 2009 John Wiley & Sons, Ltd and Eating Disorders Association.