The tracking system is for patients identified in the Creutzfeldt Jakob Disease (CJD) lookback notification initiative established in January 1995 as part of the lookback notification of all Department of Veterans Affairs (VA) patients who may have received certain lot numbers of blood derivatives or blood components produced from donors with CJD. Even though the Centers of Disease Control and Prevention characterized the risk of transmission of CJD from blood derivative products as 'small and immeasurable' and 'theoretical', VA believed it had an ethical obligation to inform patients of the exposure to potentially contaminated blood components or plasma derivative products while under VA's care. The patients were notified. The Veterans Health Administration (VHA) established a tracking system for individuals who received these products to determine if there was an increase in VA CJD cases. Every two years, the VHA National Infectious Diseases Service updates the status of patients who had previously been identified through the VA CJD lookback notification initiative. The Creutzfeldt-Jakob Disease Lookback Dataset (CJDLD) is a prospective collection of data; requests for individual reports are not accepted.