Purpose: Pseudomyxoma peritonei (PMP) originating from an appendiceal mucinous neoplasm remains a biologically heterogeneous disease. The purpose of our study was to evaluate outcome and long-term survival after cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) consolidated through an international registry study. Patients and Methods: A retrospective multi-institutional registry was established through collaborative efforts of participating units affiliated with the Peritoneal Surface Oncology Group International. Results: Two thousand two hundred ninety-eight patients from 16 specialized units underwent CRS for PMP. Treatment-related mortality was 2% and major operative complications occurred in 24% of patients. The median survival rate was 196 months (16.3 years) and the median progression-free survival rate was 98 months (8.2 years), with 10- and 15-year survival rates of 63% and 59%, respectively. Multivariate analysis identified prior chemotherapy treatment (P = .001), peritoneal mucinous carcinomatosis (PMCA) histopathologic subtype (P = .001), major postoperative complications (P = .008), high peritoneal cancer index (P = .013), debulking surgery (completeness of cytoreduction [CCR], 2 or 3; P = .001), and not using HIPEC (P = .030) as independent predictors for a poorer progression-free survival. Older age (P = .006), major postoperative complications (P = .001), debulking surgery (CCR 2 or 3; P = .001), prior chemotherapy treatment (P = .001), and PMCA histopathologic subtype (P = .001) were independent predictors of a poorer overall survival. Conclusion: The combined modality strategy for PMP may be performed safely with acceptable morbidity and mortality in a specialized unit setting with 63% of patients surviving beyond 10 years. Minimizing nondefinitive operative and systemic chemotherapy treatments before definitive cytoreduction may facilitate the feasibility and improve the outcome of this therapy to achieve long-term survival. Optimal cytoreduction achieves the best outcomes.