A 41-year-old man had a 6 x 6 x 5-disk diameter amelanotic tumor in the posterior fundus. The clinical and fluorescein angiographic appearance suggested a benign retinal vascular tumor, although amelanotic choroidal melanoma and retinoblastoma were diagnostic possibilities. An incisional 48-hour radioactive phosphorus (32P) uptake test was performed and the result showed an increased uptake over the tumor mass of 100% as compared to the control quadrants. The globe was enucleated and the pathologic diagnosis was isolated astrocytic glioma of the retina with minimal, if any, malignant potential. The highly developed vascular system of the tumor probably contributed to the false-positive test result.