Protein C deficiency is one of the most important cause of thrombosis during early infancy and may have different ways of presentation. We have collected 11 patients, 10 with portal vein thrombosis, 1 with thrombosis of both right and left jugular vein after a Broviac catheter insertion. As far as the time and the trigger event are concerned, we suppose that the thrombosis took place in 9 patients during the neonatal period. Seven out of the nine patients with portal vein thrombosis had umbilical catheterization during neo-natal period (4 due to hyperbilirubinemia and 3 due to prematurity), one patient received surgery in the first day of life because anorectal malformation, whereas we have no information about the last patient. The early symptoms of thrombosis started within the first year of life in 5 patients and within the forth year in 4. In 9 patients the symptoms were, in sequence: splenomegaly, esophageal varices and hypersplenism. The diagnosis of protein c deficiency has been made from 6th month to 14th year after the trigger event. Protein c biological activity values was X = 47% ±9.03 (n.v. 65-128%) and Protein c antigen was X = 51% ±14 (n.v. 68-110%). Antithrombin III (ATIII) was slightly decreased in 7 patients, protein s in 2, factor v below the normal in 3, whereas FII was in the normal range. Four of these patients received Protein c concentrate (Immuno - Vienna), together with heparin treatment during vascular surgery (spleen, renal vein, shunt). In conclusion we can say that all our patients had a more or less marked first type Protein c congenital deficiency. From the pathogenetic point of view we can speculate that the mechanical and chemical action on the vessell wall due to the catheter and the fluid, associated with the prematurity related disorders, can trigger the thrombotic mechanism.