Objective: This study tests a Stabilizing Group Treatment protocol, designed for the management of the long-term sequelae of child abuse, that is, Complex Posttraumatic Stress Disorder (Complex PTSD). Evidence-based treatment for this subgroup of PTSD patients is largely lacking. This stabilizing treatment aims at improving Complex PTSD using psycho-education and cognitive behavioral interventions. Method: Thirty-six patients with a history of childhood abuse, Complex PTSD and severe co-morbidity entered a 20-week treatment with pre-, post-, and follow-up-assessments. Results: Improvement was found for PTSD and borderline symptoms. Post-treatment 64% and after 6 months 78% of patients no longer met criteria for Complex PTSD. Conclusions: This open study indicates both the feasibility of investigating treatment outcome and the initial efficacy of stabilizing group treatment in severely ill patients with Complex PTSD related to childhood abuse. © 2010 Elsevier Ltd.