Reemerging infectious diseases are infections that had decreased in incidence in the global population and were brought under control through effective health care policy such as vaccination, but more recently, began to resurge as a health problem due to many reasons. Measles, rubella, mumps and pertussis are the examples. Immunization with MMR (measles, mumps, rubella) and pertussis vaccine has contributed to marked decrease in measles, mumps, rubella and pertussis incidence worldwide. In Korea, measles and rubella almost disappeared after the introduction of 2 doses of MMR immunization schedule. Recently, these infections have been reemerging in many countries with low vaccination rates and can be introduced again in Korea. However mumps and pertussis outbreaks are reported among fully vaccinated populations. Declining vaccine effectiveness, an increased awareness and surveillance of the disease or improved laboratory diagnostic tools had been suggested as possible causes. For the clinicians, it is difficult to diagnose these reemerging infectious diseases partly because of few experience of typical cases of measles and rubella or partly because of modification of clinical symptoms and signs of infectious diseases in immunized population. In this article, the diagnosis of measles, mumps, rubella and pertussis will be reviewed in the aspects of clinical characteristics, serologic methods, virus isolation, and polymerase chain reaction.