Previous studies demonstrated clusters of cases of IDDM occurring 24 to 48 months after immunization with the hemophilus, pertussis and combined measles mumps rubella vaccines. Data was analyzed to determine if similar clustering of cases of IDDM occurred after immunization with the hepatitis B vaccine. Methods: Data on the incidence of IDDM from hepatitis B immunized and unimmunized cohorts of children was analyzed for the presence of clusters occurring after hepatitis B immunization. Results: Data from Italy, France, and New Zealand indicated rises in the incidence of IDDM occurred between 24 to 48 months after the introduction of the hepatitis B immunization in young children. Conclusion: Several different vaccines as well as infections with natural mumps virus are followed by clusters of cases of IDDM that occur about 24 to 48 months after immunization. This suggests a similar mechanism of action, possibly the triggering of a progressive autoimmune phenomenon.