Peritoneal seeding from colorectal cancer has a very poor prognosis and is relatively resistant to systemic chemotherapy. We performed a phase I/II trial to investigate the feasibility and effectiveness of extensive cytoreductive surgery in combination with intra-operative hyperthermic intraperitoneal chemotherapy (HIPEC) in these patients. 29 patients with peritoneal carcinomatosis of colorectal origin without evidence of distant metastases underwent cytoreductive surgery and intra-operative HIPEC with mitomycin-C (MMC), followed by systemic chemotherapy with 5-fluorouracil (5-FU)/leucovorin. Surgical complications occurred in 11 patients (38%). One patient died directly related to the treatment, resulting in a mortality rate of 3%. MMC toxicity existed mainly of leucocytopenia (in 15 patients; 52%). After a median follow-up of 38 months (range 26-52 months) we found a 2- and 3-year survival rate (Kaplan-Meier) of 45 and 23%, respectively. Extensive cytoreductive surgery and HIPEC is feasible in patients with peritoneal seeding of colorectal cancer. First results suggest that a higher median survival could be achieved compared with conventional palliative surgery and systemic chemotherapy, therefore a randomised phase III study is now being conducted.