The United Kingdom General Practice Research Database (GPRD) is an office-based, computer-generated, medical resource designed from its inception to be used for epidemiologic research. A distinct version of the GPRD is maintained by the Boston Collaborative Drug Surveillance Program and has been the source of more than 130 scientific articles primarily addressing drug safety issues. We reviewed evidence related to the validity of the GPRD. Specifically, with our extensive experience with this automated database, we evaluated the quality and completeness of the data that it contains.