A 69-year-old female with seropositive rheumatoid arthritis presented with progressive cognitive decline following treatment with infliximab and methotrexate. Cranial MRI showed non-enhancing white matter signal abnormality consistent with demyelination was seen in the antero-inferior left frontal lobe extending into the frontal opercular white matter and into the left temporal lobe white matter. Similar appearances were seen in the inferomedial right frontal lobe. Brain biopsy showed histological changes consistent with progressive multifocal leukoencephalopathy. The cerebrospinal fluid polymerase chain reaction was negative but brain tissue polymerase chain reaction was positive for JC virus. This case highlights the association of infliximab with progressive multifocal leukoencephalopathy in a patient with known seropositive rheumatoid arthritis.