The neurologic manifestations of Legionnaires' disease were reviewed in this paper. Nine (42.9%) of 21 patients seen at this institution had neurologic abnormalities during acute infection, comparable to 52% of patients found in the literature. Abnormal mentation was most common, occurring in all our patients and in 29.6% of patients in the literature. Encephalopathy disproportionate to metabolic disturbances varied from mild confusion to coma, was not associated with increased mortality, and tended to resolve with acute illness although some patients reported persistent memory defects. Rarely did these changes in mentation precede the development of pulmonary infiltrates. Headache occurred in two (22.2%) of our patients and in 28.7% of those in the literature. Headache, noted in many febrile illnesses, is common but nonspecific in Legionnaires' disease. Other neurologic abnormalities including cerebellar dysfunction and focal deficits were relatively infrequent and tended to persist beyond resolution of clinical infection. In some cases these neurologic derangements may have occurred coincidentally with Legionnaires' disease. Diagnostic evaluations and autopsies were frequently normal, nonspecific, or revealing of pathology unrelated to infection. Only two patients had evidence of direct invasion of the central nervous system by Legionella, and the cause of encephalopathy and neurologic abnormalities in most cases remains unclear. Patients with neurologic abnormalities and Legionnaires' disease deserve full evaluation to exclude other entities. Only encephalopathy appears to be a characteristic manifestation of Legionnaires' disease.