A rapid proliferation of registries has occurred during the last 20 years. Given the long-term commitment of resources associated with registries and limited public health funding, proposals for new registries should be carefully considered before being funded. A registry is defined as a data base of identifiable persons containing a clearly defined set of health and demographic data collected for a specific public health purpose. Criteria for evaluating whether a registry is needed, feasible, or the most effective and efficient means of collecting a specific set of health data are presented. They include an evaluation of the stated purpose; a review of the function, duration, and scope of the registry; consideration of existing alternative data sources; an assessment of the practical feasibility of the registry; the likelihood of sufficient start-up and long-term funding; and an evaluation of the cost effectiveness of the registry. Creating a public health registry is a complex process. A range of technical and organizational skills is required for a registry to be successfully implemented. Eight requirements are identified as crucial for the successful development of a new registry. They include an implementation plan, adequate documentation, quality control procedures, case definition and case-finding (ascertainment) procedures, determination of data elements, data collection and processing procedures, data access policy, and a framework for dissemination of registry data and findings.