To describe the clinical and pathologic features of two HIV-1-infected children with progressive multifocal leukoencephalopathy (PML). Case report. University-affiliated, public-health trust hospital. Two HIV-1-infected children with PML are described. A 13-year-old girl, presumed to be congenitally infected with HIV-1, presented with dysarthria and paresthesias of the tongue and chin that evolved rapidly to dementia, muteness and severe spastic quadriparesis. The other patient, a 10-year-old boy who developed HIV-1 infection from a blood transfusion at the age of 3 years, presented with a facial palsy with subsequent development of right hemiparesis and aphasia. Brain biopsy in the first child and autopsy in the second confirmed the diagnosis of PML. In both patients, the CD4 T-lymphocyte count was Conclusion. Despite seroepidemiological studies suggesting that the majority of individuals are infected with JC virus during childhood, PML is rare in children with impaired cell-mediated immunity. Our patients illustrate that PML is among the neurological complications of HIV-1 infection in children.