Peritoneal carcinomatosis represents a devastating form of cancer progression with a very poor prognosis.Its complex pathogenesis is represented by a dynamic process comprising several steps.To the best of our knowledge pathogenesis can be partly explained by 3 major molecular pathways: (1) dissemination from the primary tumor;(2) primary tumor of peritoneum;and (3) independent origins of the primary tumor and peritoneal implants.These are not mutually exclusive and combinations of different mechanisms could occur inside a single case.There are still several aspects which need explanation by future studies.A comprehensive understanding of molecular events involved in peritoneal carcinomatosis is of paramount importance and should be systematically pursued not only to identify novel strategies for the prevention of the condition,but also to obtain therapeutic advances,through the identification of surrogate markers of prognosis and development of future molecular targeted therapies. Peritoneal carcinomatosis represents a devastating form of cancer progression with a very poor prognosis. Its complex pathogenesis is represented by a dynamic process comprising several steps. To the best of our knowledge pathogenesis can be partially explained by 3 major molecular pathways: (1) dissemination from the primary tumor of peritoneum; and (3) independent origins of the primary tumor and peritoneal implants. These are not mutually exclusive and combinations of different mechanisms could occur inside a single case. There are still several aspects which need explanation by future studies. A comprehensive understanding of molecular events involved in peritoneal carcinomatosis is of paramount importance and should be systematically pursued not only to identify novel strategies for the prevention of the condition, but also to obtain therapeutic advances, through the identification of surrogate markers of prognosis and development of future molecular targeted therapies.