Progressive multifocal leukoencephalopathy (PML) is a rare demyelinating disease of the central nervous system caused by the JC virus that occurs in the setting of immunosuppression. A 38-year-old female lung transplant recipient at our institution received treatment for episodes of acute rejection with steroids, anti-thymocyte globulin and alemtuzumab, in addition to maintenance immunosuppression. She was diagnosed with PML 13 months after the last episode of rejection, for which she had received alemtuzumab. Despite attempted treatment with cidofovir followed by mirtazapine, PML progressed, and she ultimately died of an acute pulmonary infection and respiratory failure. We provide a detailed clinical and radiographic description of PML in a lung transplant patient and highlight its potential relationship to intensive immunosuppression, as the disease developed in the setting of markedly reduced CD4 counts.