Five different descriptions quantitating peritoneal carcinomatosis are available: the Lyon staging system, the Peritoneal Cancer Index (PCI), the Japanese Research Society for Gastric Cancer carcinomatosis staging (JRSGS), the Dutch simplified peritoneal carcinomatosis assessment and the Completeness of Cytoreduction Score (CCR). These five staging systems are described and discussed. Combinations of these to achieve a complete description of peritoneal lesions prior to and following treatment assist in a correct prognostic assessment for these patients and in a selection of treatment options.