The epidemiology of Guillain-Barre syndrome (GBS) and the associations of GBS with influenza vaccination are described based on review of three types of epidemiological data: case-control studies, incidence rate studies of GBS in well-defined populations, and surveillance data from a sentinel neurologist surveillance system of GBS in the United States. These data indicate that the crude annuai incidence rate of GBS per 100,000 people ranges from 0.6 to 1.9 in different populations in widely scattered areas of the world. In general, incidence rates are higher with advancing age until about 75 years, higher for men than women, and higher for whites than blacks. No specific HLA antigen has been significantly associated with GBS in general, although HLA AW 30 and AW 31 have been associated with chronic relapsing polyneuritis. Important trigger agents of GBS include nonspecific respiratory and gastrointestinal infections and cytomegalovirus infection. Influenza infection and influenza vaccinations are not generally important trigger agents. A major exception to this is the occurrence of just under 1 excess case of GBS per 100,000 AINew Jersey influenza vaccinations administered in the United States, 1976States, -1977. A significant excess risk of GBS was not observed after administration of influenza vaccine in 1978-1979 and 1979-1980. The differences between the contents of and immunological reaction to A/New Jersey influenza vaccine and the more recent influenza vaccines deserve further study.