Many studies of population health, clinical epidemiology, and health services can be supported by a population-based research registry. Such a registry accurately defines the health insurance status for each individual over many years, magnifying the effectiveness of a cross-sectional registry (typically relevant for only a short duration) used in the administration of a health insurance plan. A research registry can distinguish between "well" individuals (no contact with the health care system), loss to follow-up (ineligibility associated with leaving the insurance plan), loss of continuity (two or more unlinked registrations over time for the same person), and mortality. The Manitoba research registry was developed to facilitate longitudinal studies; working within strict confidentiality controls, identifiers for each individual known to Manitoba Health since 1970 can be retrieved and a single unique identifier assigned. Careful reporting of changes in family registration numbers has enabled tracing area of residence, marital status, and family characteristics; results are equivalent to a daily census of the province. This article provides details on source materials, design, and quality of the registry, highlighting its value both for the development of integrated population health information systems and for research in general.