A brief review of the atypical measles syndrome is presented. In addition to the clinical aspects of the disease, including the differences with classical measles, the biologic features of the condition will be described. A series of queries relating the syndrome will then be raised and, whenever possible responded to. Thus, it appears that the atypical measles syndrome is possibly not contagious. Immune complexes formation may be critical to the pathogenesis of this disease. This condition is not often severe and very rarely fatal. This syndrome may be exceptionally related with the live attenuated anti-measles vaccine. In spite of a common belief on the absence of immune waning, it is possible that humoral waning may play an important role in the atypical measles syndrome.