In a nosocomial outbreak of Campylobacter jejuni infection 11 newborn infants (7 female, 4 male) had meningitis. The outbreak was caused by a single strain of C jejuni, as demonstrated by biotyping (biotype I), serotyping (LAU 7/PEN 18 on heat-stable antigens, a new serotype on heat-labile antigens), and the identical susceptibility pattern and outer-membrane-protein profile on sodium dodecyl sulphate/polyacrylamide gel electrophoresis. Specific antibodies against the outbreak strain (enzyme-linked immunosorbent assay and Western blot) developed in all the babies. They were treated with gentamicin and ampicillin. All but one baby, who had a moderately dilated left lateral ventricle after the meningitis, recovered well. The source of infection could not be clearly determined. Thus, C jejuni can cause serious nosocomial infection; it should be considered as a possible agent of meningitis of unknown origin, particularly in newborn infants and other compromised hosts.