A great number of locoregional treatments are currently carried out to treat a variety of locoregional neoplastic diseases. Indications are the treatment of primary and metastatic liver tumors, peritoneal mesotheliomas, peritoneal spread of ovarian carcinomas, peritoneal recurrences of gastrointestinal cancers, peritoneal spread of retroperitoneal sarcomas, melanomas and sarcomas of the limbs, some primary tumors of the brain, breast, kidney, lung, bladder. But to deal with locoregional therapy demands to clarify some features of these malignancies. At this regard, the knowing of their natural history can be crucial to guide the choice of the correct locoregional treatment. For instance peritoneal carcinomatosis is considered as a main step of disease progression for ovarian cancer and often for gastrointestinal tumors as well. However when the tumors are confined on the surface of the peritoneum, basing on their own natural history, they can be considered as localized diseases. Selected patients with peritoneal neoplastic seeding, previously considered in a preterminal condition, can be considered as candidates for curative treatment, using cytoreductive surgical tecniques (16) and hyperthermic intraperitoneal chemotherapy (19). The same can be thought about others primary or metastatatic tumors when the neoplastic deposits are confined within a definite site or region of the body. In this paper the main aspects of liver metastases and peritoneal carcinomatosis natural history, two of the most frequently recognized indications for locoregional therapy, are presented.