We report the case of a patient with isolated ocular involvement and non-Hodgkin's lymphoma (also known as reticulum cell sarcoma). Most non-Hodgkin's central nervous system lymphomas are large cell lymphomas derived from B-cells. The patient initially had iritis OD and vitreous cells OS. Eventually, rubeosis and vitritis developed OD. A systemic workup showed no extraocular lymphoma. Immunocytochemical analysis was done on the vitreous OD and detected a monoclonal B-cell population of large lymphoid cells. This case shows the frequent delay in making the diagnosis of this condition. This diagnosis must be remembered when a patient has vitreous opacities.