All acute Guillain-Barré syndrome (GBS) cases identified in the county of Uusimaa in southern Finland from 1981-1985 were analyzed. The incidence varied from 0.5 to 2.1 per 100,000 population. An antecedent event of possible etiologic significance was reported in 10% of the cases. Plasma exchange therapy was introduced during these years. Less children than expected fell ill, perhaps because of vaccinations, but a rise in the incidence of GBS in 1985 occurred during a nation-wide oral poliovirus vaccination campaign. A total of 19.4% of the patients needed respirator treatment, and plasma exchange therapy was given to 27.4% of these patients, among whom the time in respirator was shortened compared to equally affected individuals not given plasma exchange. The mortality was lower in the recent compared to the earlier period. This may be due to plasma exchange therapy.