A patient with a malignant thymoma developed systemic lupus erythematosus with neurological involvement and multiple infectious complications, including progressive multifocal leukoencephalopathy and cryptococcal meningitis. Data from this patient and studies by others are consistent with t h e concept that all cases of progressive multifocal leukoencephalopathy are associated with a defect i n cellular immunity.Malas D, Weiss S: Progressive multifocal leukoencephalopathy and cryptococcal meningitis with systemic lupus erythematosus and thymoma.