In 1991, the AIDS Task Force of the American Academy of Neurology published nomenclature and research case definitions to guide the diagnosis of neurologic manifestations of HIV-1 infection. Now, 16 years later, the National Institute of Mental Health and the National Institute of Neurological Diseases and Stroke have charged a working group to critically review the adequacy and utility of these definitional criteria and to identify aspects that require updating. This report represents a majority view, and unanimity was not reached on all points. It reviews our collective experience with HIV-associated neurocognitive disorders (HAND), particularly since the advent of highly active antiretroviral treatment, and their definitional criteria; discusses the impact of comorbidities; and suggests inclusion of the term asymptomatic neurocognitive impairment to categorize individuals with subclinical impairment. An algorithm is proposed to assist in standardized diagnostic classification of HAND. Neurology ยฎ 2007;69:1789-1799 GLOSSARY AAN ฯญ American Academy of Neurology; ADLs ฯญ activities of daily living; ANI ฯญ asymptomatic neurocognitive impairment; HAART ฯญ highly active antiretroviral treatment; HAD ฯญ HIV-associated dementia; HAND ฯญ HIV-associated neurocognitive disorders; HNRC ฯญ HIV Neurobehavioral Research Center; IADLs ฯญ instrumental ADLs; MCMD ฯญ minor cognitive motor disorder; MND ฯญ HIV-associated mild neurocognitive disorder; MSE ฯญ mental status examination.