Over a 20-month period, 3 adult and 6 pediatric patients were diagnosed with Guillain-Barré syndrome (GBS) at Groote Schuur and Red Cross Hospitals in Cape Town. All 9 GBS patients had Campylobacter jejuni biotype 2, serotype O:41 in their stools. C. jejuni infection was confirmed by ELISA testing of patient sera. Strains of this sero-biotype are rare: Only 12 such strains, including the GBS-associated strains, were recognized among 776 Campylobacter strains isolated and identified at Red Cross Hospital from March 1994 to October 1995. This is the first known association of C. jejuni biotype 2, serotype O:41 with GBS. Patients infected with this Campylobacter strain had a particularly severe form of the infection, requiring hospitalization and ventilation much longer than GBS patients infected with other Campylobacter species and patients with Campylobacter-negative stools. The O:41 Campylobacter isolates from the GBS patients are identical by phenotypic, serologic, and molecular criteria, and they are clonal.