Complex dissociative disorders (CDD) include dissociative identity disorder (DID) and the most common other specified dissociative disorder (OSDD, type 1). While consensus-based treatments for CDD are lacking in several international guidelines, patients suffering from CDD show high levels of impairment, treatment utilization and costs. Migrants and refugees often present risk factors for trauma-related and dissociative disorders and need effective and culturally adapted treatments. Schema Therapy (ST) is an integrative psychotherapy that has been recently proposed as a treatment for CDD. This case study examined the process of individual ST, in a three phases-based approach, with a 38-year-old male Yemeni refugee with OSDD, type 1, posttraumatic stress disorder and borderline personality disorder. The treatment was provided in a Western country and the setting included two Western therapists (co-therapy) and an Arabic interpreter/cultural mediator. We assessed the patient's change by using self-report assessments of dissociative and PTSD symptoms, cognitive schemas over 2-year and 4-months treatment periods and a 6-months follow-up. Posttreatment and follow-up reliable change analyses showed significant improvements in dissociative and PTSD symptoms as well as in some cognitive schemas. Despite any firm conclusion cannot be drawn due to the limitations of this study (i.e., single case study), the findings suggest that ST integrated in a phase-oriented approach may be an effective treatment for CDD. Additionally, our study provides some preliminary elements about cross-cultural validity of the schema modes construct as well as cross-cultural effectiveness of ST. More research based on larger samples and specific cross-cultural focused design is needed to confirm these assumptions.