Health care in Sweden usually focuses on single diseases and is less prepared to treat people with multimorbidity. Combining different national quality registries (NQR) can provide a broader picture of health care, preventive care, and health-promoting care of older people with multimorbidity. The aim of this study was to explore how NQRs can be used in gerontological health care research. A descriptive mixed-method study, including a case report and statistical analysis, was performed. Nine National Quality Registries, three health registries and a social care registry maintained by the Swedish government were individually matched to an older population (birth year 1896 to 1958) in the Swedish Twin Registry (n≈44000). Factor analysis demonstrated the people tended to fall into one of 4 clusters of registries: stroke/dementia/hip, heart/diabetes, arthritis-related, and other. Men were more highly represented in the heart/diabetes cluster. People in the arthritis cluster had the lowest mean age; people in the stroke/dementia/hip cluster had the highest mean age. 161 people were identified as “most ill elderly” (according to the definition by the Swedish government). Two of them were randomly selected for case reports. Each case appeared in 6–7 of the health quality registries, providing sufficient information to track their progression through the health care system until the point of death. The results highlight both pros and cons of using the quality registries as the basis for analysis and “registry-enriched” research designs, but more research needs to be performed to understand how NQRs can be used in gerontological research.