Snider was the first to recognize and report that HIV infection affected the central nervous system (Snider et al., 1983). Shortly after this a syndrome of dementia was described in people with advanced HIV infection (Navia, Jordan and Price, 1986; Navia et al., 1986). This was followed by reports of cognitive deficits in asymptomatic individuals with HIV infection (Grant et al., 1987). There was, initially, concern that the onset of cognitive impairment occurred early in the infection, and there were fears that the dementia was far more common than now appears to be the case. The dementia associated with HIV has been known as AIDS dementia complex (ADC), sub-acute encephalitis, HIV encephalopathy, HIV-1 associated cognitive motor complex and most recently HIV-1 associated dementia. These terms are not strictly inter-changeable but have often been used that way. It is therefore not surprising that they have often caused misunderstanding. This confusion in terminology initially made the interpretation of research difficult. More recently, the careful observations of clinicians and development of carefully defined diagnostic criteria has enabled researchers to form conclusions about many issues relating to the HIV dementia.