Listeria monocytogenes rhombencephalitis has never been studied in a significant group of patients. We describe 14 adult cases who were seen over a 10-year period. A biphasic illness was characteristic: (1) prodromes (5-15 days) with malaise, fatigue, headache, nausea or vomiting, and fever; (2) cranial nerve palsy with facial palsy, diplopia, dysphagia, dysarthria, usually multiple. Meningism and hemi- or tetraparesis were present in 11 patients and cerebellar dysfunction in 9 patients. In 4 cases, CT showed widening of the brain stem with disappearance of the surrounding cisterns. The cerebrospinal fluid was abnormal in all patients in whom this investigation was done (pleocytosis, elevation in protein content). The patients received antibiotic therapy for 2-6 weeks. In the 9 patients who recovered, the neurological dysfunction improved within 2 days to 1 week of the initiation of therapy. There were 5 deaths. At autopsy in 2 cases, there was severe purulent meningitis and rhombencephalitis with predominantly polymorphonuclear cellular infiltration in 1 case, while numerous microabscesses in the midbrain, pons and medulla were observed in the other. We conclude that L. monocytogenes infection should be considered in patients who develop fever and focal neurological signs particularly localized to the brain stem.