The right eye of a 4-month-old girl with a large, unilateral, sporadic retinoblastoma was enucleated. The tumor was unusual because it contained Flexner-Wintersteiner rosettes with extremely large lumina. Smaller rosettes and undifferentiated tumor cells were observed within the lumina. Also of importance were cells resembling glial cells which were intermixed with more typical cuboidal retinoblastoma cells. These cells had electron microscopic features typical of glial cells and stained positively for glial fibrillary acidic protein in immunohistochemical studies. Rosettes and glial cells continued to be observed in the tumor carried in tissue culture through two passages over a 7-month period. This tumor is presented because of its unusual rosette structures and because it confirms recent reports describing a glial cell component in retinoblastoma.