Primary central nervous system lymphoma (PCNSL) is a rare variant of extra-nodal diffuse large B-cell lymphoma (see this term) involving the brain, leptomeninges, eyes, or spinal cord, and characterized typically by a solitary tumor that, depending on its location, can lead to a variety of symptoms such as headaches, nausea, vomiting (and other signs of raised intracranial pressure), focal neurologic deficits, neuropsychiatric and ocular symptoms, seizures and personality changes. It can occur in the immunocompetent (usually in the 6th decade of life) but is more common in the immunocompromised (especially in HIV-infected patients) and has an aggressive disease course.