We describe the age- and sex-specific incidence of Guillain-Barre syndrome (GBS) in Harbin, China, based on the information from a prospective survey among a well-defined large population during one year. A network of physicians reported incident patients with a GBS diagnosis from a general population of 5.4 million inhabitants in Harbin, China, during the period from 1 October 1997 to 30 September 1998. Each reported patient was examined by senior neurologists and the GBS diagnosis was validated according to standard diagnostic criteria. All GBS patients were followed-up for six months after onset. Admission registers at all hospitals in Harbin were also checked afterwards for screening patients with a GBS diagnosis who might have been missed. During the study period, 79 patients with a GBS diagnosis were reported. After validation, the GBS diagnosis was confirmed in 70 patients. Another GBS patient was found through the screening of admission registers at hospitals. Among them, 36 GBS patients were residents in Harbin and the other 35 patients were from geographical areas out of Harbin. The GBS incidence, age-adjusted to the European standard population, was 0.66 (95% CI 0.46-0.91) per 100,000 person-years, with a male to female ratio of 1.4. The highest GBS incidence was found in the youngest age-group and the incidence among the elderly was remarkably lower than those reported from other populations in Western countries. Possible explanations for the distinct pattern of age-specific incidence of GBS are discussed. Further studies are needed.