Background/Aim: The purpose of this study was to prove the effect of complete surgical staging of patients with mucinous borderline ovarian tumors (mBOTs) especially appendectomy on progression-free survival (PFS) and overall survival (OS). Patients and Methods: The database of 14 gynecological oncology departments from Turkey and Germany were comprehensively searched for women who underwent primary surgery for an ovarian tumor between January 1, 1998, and December 31, 2015, and whose final diagnosis was mBOT. Results: A total of 364 patients with mBOT with a median age of 43.1 years were included in this analysis. The median OS of all patients was 53.1 months. The majority of cases had Stage IA (78.6%). In univariate and multivariate analyses, radical surgery, omentectomy, appendectomy, lymphadenectomy, and adding adjuvant chemotherapy were not independent prognostic factors for PFS and OS. Furthermore, FIGO stage (>= IC vs.