Objective -To analyse the causes of non resectability of peritoneal carcinomatosis (PC) of non-appendiceal colorectal carcinomas, discovered only at the time of the laparotomy. Summary background data -The combination of a maximal cytoreductive surgery (resecting tumor deposits > 1 mm in diameter) with intraperitoneal chemohyperthermia results in cure a significant number of patients. Complete resection of the PC is the determining factor of this time-consuming and resource-consuming therapy. Unfortunately, it has not been possible, so far, to safely predict complete resectability before carrying out the laparotomy. Methods -All patients with colorectal PC who had undergone a laparotomy in order to receive this new treatment, but who finally presented a non completely resectable P C were included in our study. Their preoperative parameters were retrospectively studied and compared to matched number of patients who had successfully undergo ne this treatment. Results -29 patients had incomplete resection PC at laparoto my. They were compared with 29 matched patients who underwent a complete resecti on of the PC. The factors predicting non resectability were, in decreasing order of frequency: presence or persistence of an ascitis just before the laparotomy (P = 0.0008), progression of the PC while on neo-adjuvant chemotherapy (P = 0.0 1), abnormal CT-imaging (P = 0.03), and sub-occlusive syndrome (P = 0.05). The se parameters were partially inter-related. Conclusion -The persistence of asc itis and any progression of the disease while on chemotherapy are important pred ictive factors of incomplete resectability of nonappendiceal colorectal PC. Objective -To analyze the causes of non resectability of peritoneal carcinomatosis (PC) of non-appendiceal colorectal carcinomas, discovered only at the time of the laparotomy. Summary background data -The combination of a maximal cytoreductive surgery (resecting tumor deposits> 1 mm in Complete resection of the PC is the determining factor of this time-consuming and resource-consuming therapy. Unfortunately, it has not been possible, so far, to safely predict complete resectability before carrying out the laparotomy. Methods - All patients with colorectal PC who had undergone a laparotomy in order to receive this new treatment, but who finally presented a non completely resectable PC were included in our study. Their preoperative parameters were retrospectively studied and compared to matched number of patients who had successfully ago ne this treatment. Results -29 patients had inc The factors predicting non resectability were, in decreasing order of frequency: presence or persistence of an ascitis just before the laparotomy (P = 0.0008), progression of the PC while on neo-adjuvant chemotherapy (P = 0.0 1), abnormal CT-imaging (P = 0.03), and sub-occlusive syndrome Conclusion -The persistence of asc itis and any progression of the disease while on chemotherapy are important pred ictive factors of incomplete resectability of nonappendiceal colorectal PC.