The WHO launched a multicentre study to explore the nature and prevalence of HIV-1-associated neurological, psychiatric, and neuropsychological abnormalities in persons living in different geographical and sociocultural contexts. The study is being conducted in Brazil, Germany, Kenya, Thailand, the United States of America, and Zaire. A comprehensive instrument for the collection of neuropsychiatric data (including a battery of neuropsychological tests suitable for cross-cultural use) has been developed, and the feasibility of the recruitment and assessment procedure designed for the main phase has now been demonstrated.