THE SYNDROME WAS CHARACTERIZED BY A TRIAD OF HISTOPATHOLOGICAL FEATURES, INCLUDING DEMYELINATION, ABNORMAL OLIGODENDROGLIAL NUCLEI, AND GIANT ASTROCYTES. BY THE END OF THE 20TH CENTURY, PREDISPOSING ILLNESSES FOR PML CHANGED DRAMATICALLY. HIV/AIDS ACCOUNTED FOR MORE THAN 90%. ENTERING A NEW ERA, PML WITH THE USE OF BIOLOGIC AGENTS. INTEREST MAGNIFIED BY PML WITH OTHER BIOLOGIC AGENTS, EFALIZUMAB, BELATACEPT, RITUXIMAB, ALEMTUZUMAB, MYCOPHENOLATE MOFETIL, FINGOLIMOD AND BG12.