We evaluated the putative factors for the onset of Guillain-Barré syndrome (GBS) in Harbin, China by a case-control study based on the information from GBS patients identified from a population-based incidence survey, which is the first study of this kind in China. Sixty-nine GBS patients were identified during a 1-year period from 1 October 1997 to 30 September 1998, and they were matched with 69 controls for gender and age (+/-5 years). GBS diagnosis was validated by senior neurologists and GBS patients were followed up for 6 months after onset. Odds ratio (OR) and 95% confidence intervals (CI) for each putative factor for the onset of GBS were calculated and compared between GBS cases and controls. Precedent respiratory infections within 2 months before onset were found to be significantly more frequent in GBS patients than in controls (OR = 1.68, 95% CI: 1.21-2.33). Although the number of cases with gastroenteritis among GBS patients was more than double of that in the controls, the difference was not statistically significant (OR = 2.25, 95% CI: 0.73-6.96). Other putative factors as well as characteristics regarding family situation, education level, occupation, etc., were not found to be statistically different between GBS patients and controls.