RecruitingThinking and Memory Problems in People With HIVBackground: \- People with human immunodeficiency virus (HIV) can sometimes develop thinking and memory problems. These problems can vary widely, from few symptoms to severe problems with memory and concentration. It initially was thought that good HIV treatment could prevent almost all HIV-related memory problems. However, even people with low HIV viral loads can have these problems. It may be caused by HIV affecting the brain and spinal fluid. It is not yet clear why HIV causes these problems and why they may be worse in some people than others. Researchers want to study people with HIV and healthy volunteers to see how HIV may affect people with only small amounts of the virus in their blood. Objectives: \- To study thinking and memory problems in individuals with HIV that is otherwise controlled with medications. Eligibility: * Individuals between 18 of age or older whose HIV has been controlled with medications for at least 1 year. * Healthy volunteers between 18 of age or older. Design: * Participants will be screened with a physical exam and medical history. Blood and urine samples will be collected. A neurological test will also be given. Participants will have a baseline imaging study of the brain. * Within 12 weeks of the first visit, participants will have a second visit. Additional blood samples will be drawn. Another brain imaging study will be performed. * Within 8 weeks of the second visit, participants will have a third visit to collect more blood samples. They will also provide spinal fluid samples, either as a single visit or a longer procedure. * After this visit, participants will return every 12 months for up to 10 years. Blood samples will be collected as needed at these visits. Thinking and memory tests and imaging studies may also be given as needed. Spinal fluid may be collected at one visit a year.