This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. With the availability of highly active antiretroviral therapy (HAART), shifts in the spectrum of HIV-related nervous system diseases are being observed. However, there has been no large-scale, comprehensive study of these manifestations and their potential pathogenesis. The CHARTER protocol was designed as an observational, non-interventional study of the nervous system complications of HIV and HAART therapy, designed to encompass a representative sample of HIV-infected patients at 6 subsites across the United States. It will have both cross-sectional and longitudinal components, and will recruit patients in all stages of HIV disease. Hypothesis: HAART will have variable effects on CNS and PNS function, dependent upon the type of regimen and patient-specific factors. Viral replication and drug resistance are important determinants in the longitudinal manifestations of disease. This study will: 1 determine if patients taking HAART have reduced risk of CNS and PNS complications of HIV infection compared to those who are na[unreadable]ve to or have stopped prior ARV. 2 determine if the CNS penetration profile of HAART is related to antiviral effects within the CNS (as measured by CSF HIV RNA levels) and to risk of HIV-associated neurological disease (as measured by cognitive function). 3 determine if the mechanism of neurocognitive damage in late stage HIV disease differs from that in earlier stages of HIV disease. 4 measure the relationship of HIV replication within the CNS (as measured by CSF HIV RNA) and of immune competence (as measured by CD4 levels) to the prevalence and incidence of syndromic HIV-related neurocognitive impairment. 5 determine the prevalence of discordant ARV resistance in HIV plasma and CSF. 6 determine if the predictors and risk factors for peripheral neuropathy from HIV differ from that of d-drug ARV neurotoxicity.