Latent John Cunningham virus reactivates in immunosuppressed individuals and rarely it can cause Progressive Multifocal Leukoencephalopathy. 67-year-old male patient was admitted to the emergency service with a complaint of seizure and he was given diazem and phenytoin therapy with a diagnosis of status epilepticus. Chronic lymphocytic leukaemia in remission was found in his anamnesis. Lesion that could be compatible with Multifocal Leukoencephalopathy was detected in brain magnetic resonance imaging with contrast, perfussion magnetic resonance imaging and magnetic resonance spectroscopy. The case died in the fifth month of follow-up. This article has presented a case of rare Progressive Multifocal Leukoencephalopathy in the course of chronic lymphocytic leukaemia.