OBJECTIVE: Evidence-based treatments are urgently needed for individuals with trauma-related dissociation (TRD), including severe dissociative disorders, the dissociative posttraumatic stress disorder (PTSD) subtype, and complex PTSD ( METHOD: We provide an interim report on an ongoing, randomized controlled trial of FSG on an international sample of 291 outpatients with dissociative identity disorder, dissociative PTSD, other specified dissociative disorders, complex PTSD, or dissociative disorder, unspecified RESULTS: Although initially comparable on outcome measures, at 6 months into the study, the Immediate FSG group showed significant improvement in emotion regulation, PTSD symptoms, self-compassion, and adaptive capacities in comparison to the Waitlist group. At 12 months, the Immediate group showed large effect size changes in these areas compared to study entry (|g|s = 0.95-1.32). The Waitlist group showed comparable improvements after accessing the FSG program for 6 months. CONCLUSIONS: This randomized controlled trial demonstrates that adding FSG to psychotherapy of individuals with TRD results in improvements in emotion regulation, PTSD symptoms, self-compassion, and adaptive functioning. (PsycInfo Database Record (c) 2025 APA, all rights reserved).