The impetus behind locality arrangements in Health Districts in the UK is discussed in terms of recent reform of the structure of health services, and in particular the greater stress on primary and community provision, and on health prevention and promotion. Implications for needs assessment and resource allocation are considered. The advantages of using localities for epidemiological monitoring and for assessing inequality are illustrated with a case study of two outer East London boroughs; the reduction of inequity is discussed with reference to the achievement of overall health gain targets.