Cognitive and neuropsychological dysfunction heralding acute cerebral infection typically evolves to delirium or coma over hours to days, excluding neurodegenerative disorders as a tenable diagnosis. For a few more indolent infections, dementia is sometimes the presenting or predominant feature. Currently, human immunodeficiency virus-associated dementia is likely the most common infectious cause of dementia, a distinction held by general paresis, the cerebral form of tertiary syphilis, for the prior century. Behavioral and cognitive disturbances are also presenting manifestations of subacute sclerosing panencephalitis, an infection with defective measles virus, and Whipple's disease, caused by the bacterium Tropheryma whipplei. Neuropsychological dysfunction is occasionally a prominent and relatively isolated presenting manifestation of cryptococcal meningitis and neurocysticercosis. Memory and concentration difficulties are common in patients with hepatitis C infection, Lyme disease, and prior West Nile virus infection. Neurobehavioral disorders may also be sequelae of acute brain infections, including community-acquired acute bacterial meningitis and viral encephalitis.