A 65-year-old woman complained of blutrred vision in the left eye. On examination of that eye, vitreous opacity and intracameral cells were found. The patients was treated with topical and systemic corticosteroids. The vitreous opacity reduced slightly but recurred. Results of a vitreous biopsy showed B-cell malignant lymphoma. After radiotherapy, the vitreous opacities diminished. Early cytologic examination of vitreous cells should be performed in patients with steroid-resistant, idiopathic uveitis.