During the period January 1978-March 1981, 2,575 cases of Guillain-Barre syndrome (GBS) were reported by participating neurologists in the national GBS surveillance system. The incidence of GBS was highest in the 50- to 74-year-old age group, but a lesser peak was observed in persons aged 15 to 35. The frequencies of antecedent respiratory (43%) and gastrointestinal (21%) illness exceeded frequencies of such illnesses in the US population (10 and 0.8%, respectively), based on survey data compiled by the National Center for Health Statistics; the differences in these frequencies of illness were similar in all seasons of the year, in males and in females, and in persons < 6, 6 to 16, 17 to 44, and > 44 years of age. Nineteen percent of adult patients for whom information was available (67% of the total) reported receiving an A/ New Jersey influenza vaccine in 1976, a lower percentage than would be expected on the basis of a survey conducted in that year. The data suggest that persons who received this vaccine have not been at increased risk and may even have been at decreased risk of acquiring GBS during the period covered by this study.