Pattern and extent of epithelial membrane antigen (EMA) immunoreactivity in ependymomas as compared to other glial tumors have only been investigated in small series. To determine sensitivity and specificity of EMA staining, 54 ependymomas were evaluated in comparison to 54 glioblastomas, 43 fibrillary astrocytomas and 21 oligodendrogliomas. Distinct punctate intracytoplasmic EMA immunoreactivity was observed in 48/54 ependymomas (89%), whereas ring-like EMA staining was observed in 17/54 ependymomas (31%). Apart from the absence in most myxopapillary ependymomas, neither staining pattern was related to tumor grade or localization. Dot-like EMA immunoreactivity was less frequently observed in glioblastomas [32/54 (59%), P<0.05 vs ependymomas], fibrillary astrocytomas [10/43 (23%), P<0.001 vs ependymomas] and oligodendrogliomas [2/21 (10%), P<0.001 vs ependymomas], whereas ring-like EMA staining was absent. Sensitivity and specificity of punctate EMA staining for the diagnosis of ependymoma as compared to other glial tumors were determined: A finding of 5 EMA dots/high-power field was associated with a sensitivity of 72% and a specificity of 81%. The presence of ring-like EMA positive structures was less sensitive (32%), but highly specific (100%). To conclude, distinct punctate and ring-like EMA staining might serve as sensitive and specific markers of ependymal differentiation in glial tumors and, thus, may aid the diagnosis of ependymoma.