Background: This study was undertaken to measure survival of patients with multicystic peritoneal mesothelioma treated by cytoreductive surgery and hyperthermic intraperitoneal chemotherapy through a multi-institutional collaboration. Methods: A multi-institutional data registry, established by the Peritoneal Surface Oncology Group, was used to identify patients with peritoneal mesothelioma and the subgroup with multicystic tumours, treated by cytoreductive surgery and hyperthermic intraperitoneal chemotherapy. Outcomes for this subgroup are reported. The primary endpoint was overall survival. A secondary endpoint was the incidence of treatment-related complications. Results: Of 405 patients with peritoneal mesothelioma, 26 (6·4 per cent) had multicystic tumours. There were 20 women and six men with a mean(s.d.) age of 42(12) years. The median peritoneal carcinomatosis index (PCI) was 14 (range 6-39). There was no perioperative mortality. Six patients developed grade III or IV complications. After a median follow-up of 54 (range 5-129) months, all 26 patients were still alive. Conclusion: Multicystic peritoneal mesothelioma appears to be a distinct subtype of peritoneal mesothelioma, where long-term survival may be achieved through cytoreductive surgery and hyperthermic intraperitoneal chemotherapy.