Progressive multifocal leukoencephalopathy (PML) is a subacute demyelinating infectious disease, caused by the human polyomavirus JC (JCV), that usually occurs in immunocompromised patients. In this setting, PML has been observed in increasing numbers of patients with hematological malignancies, mostly lymphoproliferative B-cell disorders. Despite attempts with various drugs, PML has generally remained unresponsive to treatment. We report the successful use of cidofovir in a patient who developed PML 6 months before angioimmunoblastic T-cell lymphoma (AITL) was diagnosed. To the best of our knowledge, this is the first case of PML in AITL. Our case demonstrates the expanding clinical importance of PML in hematological conditions, and neurological symptoms and/or white matter changes on central nervous system imaging should arouse the suspicion of PML and lead to rapid cidofovir introduction. Progressive multifocal leukoencephalopathy (PML) is a subacute demyelinating infectious disease, caused by the human polyomavirus JC (JCV), that usually occurs in immunocompromised patients. In this setting, PML has been observed in increasing numbers of patients with hematological malignancies, mostly lymphoproliferative B-cell disorders. Despite attempts with various drugs, PML has generally remained unresponsive to treatment. We report the successful use of cidofovir in a patient who developed PML 6 months before angioimmunoblastic T-cell lymphoma (AITL) was diagnosed. To the best of our knowledge, this is the first case of PML in AITL. Our case demonstrates the expanding clinical importance of PML in hematological conditions, and neurological symptoms and/or white matter changes on central nervous system imaging should arouse the suspicion of PML and lead to rapid cidofovir introduction.