The clinical and pathologic findings of a 9-year-old girl with retinoblastoma masqueraded as atypical intraocular inflammation are presented. Histopathologic study revealed a diffuse infiltrating retinoblastoma with seeding of tumor cells into the vitreous cavity and anterior chamber. In tumors with this growth pattern, ultrasonography is of little value. Cytologic examination of aqueous and vitreous aspirates may be misinterpreted and should be evaluated carefully. Because of the seeding of tumor cells, lactate dehydrogenase assay is of diagnostic value prior to considering definitive therapy.