The origin of cancer registries was to create clinical surveys and perform patient follow-up, the objective being to bring surgical patients back to the doctor periodically to identify recurrences. Over the past 60 years, cancer registries have continued to compile patient care data and perform patient follow-up. However, over the past decade, emphasis has been placed on the direct involvement of the cancer registry in monitoring quality of care. In contrast, stroke registries monitor the quality of care for patients, but do not follow them periodically to identify recurrences. The biology of these diseases is an intricate part of the different roles played by both types of registries, yet each has a page to take from the other's book. This article examines the manner in which these registries operate to improve the quality of patient care.