It refers to the presence of free chyle in the peritoneal cavity, also called chyloperitoneum. It may have very different causes, therefore accurate clinical investigations are necessary in order to design a correct and adequate medical-surgical therapy. The most frequent causes are: neoplastic infiltration of visceral lymphatic-lymph node structures, trauma (often of iatrogenic nature, such as, for example, during extensive lymphadenectomies in surgical therapy of kidney cancer), or lymphangiodysplasia.