Central nervous system involvement by mycosis fungoides (MF) is rare and is usually seen in advanced stages of the disease. We describe a patient with early-stage follicular MF who presented with changes in mental status. Despite an initial diagnosis of vasculitis based on clinical and brain biopsy results, the postmortem examination revealed extensive infiltration of MF cells throughout the brain with leptomeningeal involvement. This case in addition to the accompanied review of literature illustrates the importance of the awareness of central nervous system involvement by MF and highlights the need for an urgent neurologic evaluation in patients with a history of MF now presenting with neurologic signs or symptoms.