Patients with peritoneal malignancy treated by cytoreductive surgery (CRS) combined with hyperthermic intraperitoneal chemotherapy (HIPEC) are prone to develop postoperative paralytic ileus (POI). POI is associated with significant increase in both morbidity and mortality. CRS and HIPEC commonly result in prolonged POI (PPOI). The objective was to clarify the extent of PPOI in patients treated by CRS and HIPEC for peritoneal malignancy. This was a prospective multicenter study including patients operated with CRS and HIPEC at the Department of Surgery, Aarhus University Hospital, Denmark and the Peritoneal Malignancy Institute, Basingstoke, United Kingdom. A total of 85 patients were included over 5 months. Patients prospectively reported parameters of postoperative gastrointestinal function in a diary from post-operative day 1 (POD1) until discharge. PPOI was defined as first defecation on POD6 or later. Median time to first flatus passage was 4 days (range 1-12). Median time to first defecation was 6 days (1-14). Median time to removal of nasojejunal tube was 4days (3-13) and 7days (1-43) for nasogastric tube. Forty-six patients (54%) developed PPOI. Patients with PPOI had longer time to first flatus (p<0.0001) and longer time to removal of nasojejunal tube (p=0.001). Duration of surgery correlated to time to first flatus (p=0.015) and time to removal of nasogastric or nasojejunal tube (p<0.0001) but not to time to first defecation (p=0.321). Postoperative gastrointestinal paralysis remains a common and serious problem in patients treated with CRS and HIPEC.