Abstract： Objective To study the clinicopatholgical features of placental site intermediate trophoblast diseases and tumors,and to highlight their differential diagnosis.Methods The clinical characteristics and the pathological features were analyzed in 15 case of exaggerated placental site(EPS)and one case of placental site trophoblastic tumor(PSTT),and a panel of immunohistochemical markers including PLAP,HPL,HCG,CK,CEA and Ki-67 wag determined,and related literatures were reviewed.Results Morpholocally,all 15 cases of EPS and one case of PSTT mainly consists of intermediate trophoblastic cells which infiltrate into the decidua,myometrium and the walls of blood vessels.The depth of muscular layers infiltrated by EPS were less than 1/3 of myometrium,with Inild necrosis,few nuclear dysplasia and mitosis;however,that by PSTT were more than 1/3 of myometrium,with large areas of haemorrhage and necrosis,evident dysplasia and mitosis.Immunohistochemically,CK,HPL,HCG,PLAP and CEA are not useful for differentiation,while Ki67 can be helpful.Conclusion The diagnosis of EPS and PSTT and the differential diagnosis with other GTDs are based on clinical history,pathological morphology and immunohistochemical staining