This document discusses immune reconstitution inflammatory syndrome (IRIS) in patients with HIV. It provides background on IRIS, defines the two types (paradoxical and unmasked), and lists risk factors. It then discusses the pathology of IRIS and various pathogens that can cause central nervous system IRIS, including PML, cryptococcal meningitis, VZV, CMV, and mycobacteria. Specific details are provided on the clinical manifestations and imaging findings of PML-IRIS and cryptococcal meningitis-IRIS.