We report a 66-year-old man with 2-month history of dizziness and 1-month history of diplopia. Cranial magnetic resonance imaging (MRI) disclosed two solid masses, one in the right lateral ventricle and another in the fourth ventricle. A surgical biopsy was performed on the basis of safety. The diagnosis of large B-cell lymphoma was made postoperatively. The patient recovered without additional deficits and was then commenced on chemotherapy and remained well 6 months after the diagnosis. Primary B-cell lymphomas should always be included in the list of differential diagnosis of intraventricular tumors. Here we report an extremely rare case of primary central nervous system lymphoma with multifocal ventricular involvement.