AIMS: To report on treatment related toxicity and mortality in patients with pseudomyxoma peritonei (PMP) treated by cytoreduction in combination with intraoperative hyperthermic intraperitoneal chemotherapy (HIPEC) and to identify prognostic factors. METHODS: A review was performed of 103 procedures of cytoreduction and intraoperative HIPEC for PMP between 1996 and 2004. Toxicity was graded according to the National Cancer Institute Common Toxicity Criteria (NCI CTC) classification. A surgical complication was defined as any post-operative event that needed re-intervention. Pre and peroperative factors were studied on their relationship to toxicity and mortality. RESULTS: The median hospital stay was 21 days (4-149) with a treatment related toxicity of 54% and a 30 days mortality of 3%. In univariate analysis, toxicity was associated with abdominal tumour load (p<0.01), completeness of cytoreduction (p<0.01), and age (p=0.05). Surgical complications, mainly small bowel perforations/suture leaks, were the main cause of toxicity. A favourable pathology decreased mortality. CONCLUSIONS: Cytoreduction in combination with intraoperative HIPEC in PMP patients is a treatment with a relatively high toxicity, but a considerable long-term survival in selected patients. Toxicity is mainly surgery related. Concentration of cases to acquire sufficient experience and better selection on age, pathology, and extent of disease is essential to reduce treatment related toxicity and mortality.