An association of progressive multifocal leukoencephalopathy (PML) and sarc
oidosis in a 47 year-old-woman is reported. This is the third case in which
PML has been diagnosed by PCR. Clinical, biological and radiological featu
res were in agreement with previous findings in immunologically suppressed
patients. JC virus should be systematically detected by PCR in blood and ce
rebrospinal fluid (CSF) in patients with sarcoidosis presenting neurologica
l and radiological PML manifestations.