Objective:The aim of this study was to study the clinicopathological and immunohistochemical features of pilomyxoid astrocytoma(PMA).Methods:The clinical and pathologic features in six cases of PMA were analyzed.Immunohistochemical staining for glial fibrillary acidic protein(GFAP),synaptophysin(Syn),Chromogranin A(CgA),cytokeratin(AE1/AE3),epithelial membrane antigen(EMA)and Ki67 was performed on paraffin-embedded sections.Results:Among the six cases,five occurred in female patients,one was male,the age at diagnosis ranged from 2 to 15 years.Four cases were located in the hypothalamic area and optic pathway,one case in the third ventricle,and one case in left parietal lobe.On imaging,PMAs often appears as well-circumscribed mass.Microscopically,the tumor was composed of monomorphous bipolar(piloid)cells setting in a prominent myxoid background with an angiocentric radiating growth pattern in some areas.PMA lacked biphasic pattern,Rosenthal fibers and eosinophilic granular bodies which were usually typical in a classic pilocytic astrocytoma(PA).Immunohistochemcal study showed that the tumor cells were diffusely positive for GFAP.Syn positive staining was observed in one case.The Ki67 labeling index measured less than 5%.Conclusion:PMA is a distinct aggressive variant of pilocytic astrocytoma with special histological and immunohistochemical features.It is typically a rare tumor of early childhood.Immunohistochemical staining for GFAP and Syn is helpful in differential diagnosis. Objective: The aim of this study was to study the clinicopathological and immunohistochemical features of pilomyxoid astrocytoma (PMA). Methods: The clinical and pathologic features in six cases of PMA were analyzed. Immunohistochemical staining for glial fibrillary acidic protein (GFAP), synaptophysin ( Syn), Chromogranin A (CgA), cytokeratin (AE1 / AE3), epithelial membrane antigen (EMA) and Ki67 performed on paraffin-embedded sections. Results: Among the six cases, five occurred in female patients, one was male, the age at diagnosis ranged from 2 to 15 years. Fours cases were located in the hypothalamic area and optic pathway, one case in the third ventricle, and one case in left parietal lobe. On imaging, PMAs often appear as well-circumscribed mass. Microscopically , the tumor was composed of monomorphous bipolar (piloid) cells setting in a prominent myxoid background with an angiocentric radiating growth pattern in some areas. PMA lacked biphasic pattern, Rosenthal fibers and eosinophilic granular bodies which Immunohistochemcal study showed that the tumor cells were diffusely positive for GFAP.Syn positive staining was observed in one case. Ki67 labeling index measured less than 5%. Conlusion: PMA is a distinct aggressive variant of pilocytic astrocytoma with special histological and immunohistochemical features. It is typically a rare tumor of early childhood. Immunohistochemical staining for GFAP and Syn is helpful in differential diagnosis.