Objective    To study the pathology of primary neuroectodermal tumor (PNET)

and its diagnostic standards and prognostic factors.     Methods    Expression of CD99，FLI-1，Syn，NSE，S-100，NF，and Vim was detected  in PNET tissues stained with HE and immmunohistochemistry (En Vision method). Survival rate of 33 PNET patients with complete clinical information was analyzed with COX regression analysis method.     Results    The positive expression rate of CD99

FLI-1

Vim，Syn，NSE and s-100 was 88.57%

51.43%

91.42%，48.57%，45.71%，and 22.86%，respectively. The sensitivity of combined CD99 and FLI-1 was 100%. However

NF was not expressed in all PNET tissues. When other factors were unchanged，no difference was found in the effect of age on the survival rate of patients. However，a significant difference was observed in the effect of PNET site and its treatment modalities on the survival rate of patients (P0.05).     Conclusion    Routine pathologic and immunohistochemical examination can provide diagnostic evidence of PNET. Detection of CD99 and FLI-1 expression with immunohistochemistry can increase the diagnostic sensitivity of PNET. The main factor affecting the prognosis of PNET is its primary site and treatment modality rather than the age of patients.