The accurate diagnosis of a juvenile granulosa cell tumor (JGCT) can be challenging, as these neoplasms often exhibit morphologic features that overlap other ovarian neoplasms. In addition, the immunohistochemical profile exhibited by JGCT is fairly nonspecific and typically includes reactivity for CD99. Recently, we noted that JGCTs can show immunohistochemical expression of Fli-1, a transcription factor expressed by Ewing sarcoma, a neoplasm that is occasionally in the differential diagnosis of JGCT. We evaluated a series of JGCTs to determine whether Fli-1 is commonly expressed by these tumors and whether they demonstrate chromosomal arrangements in EWSR1. Cases diagnosed as JGCT (n=11) were immunohistochemically evaluated for expression of Fli-1 and CD99. Fluorescence in situ hybridization was performed on all cases to search for chromosomal rearrangements in EWSR1. All 11 of our cases exhibited positive immunohistochemical staining for Fli-1 and CD99. None of the cases demonstrated rearrangement in EWSR1 by fluorescence in situ hybridization. In cases of JGCT that cannot be reliably distinguished from Ewing sarcoma based on morphology and immunohistochemistry alone, fluorescence in situ hybridization testing for EWSR1 rearrangements seems to be a useful diagnostic adjunct for their separation.