(1) Neurologic complications remain a significant problem in bacterial endocarditis. Of 218 patients with endocarditis, 84 (39%) had a neurologic complication and 58% of these 84 patients died. In contrast, the mortality rate was only 20% among those endocarditis patients without neurologic complications. (2) Of the neurologic complications, cerebral embolism is the most frequent and important. An embolic stroke occurred in 37 (17%) of our patients, with 30 of these patients dying. Emboli are important not only in terms of the direct morbidity and mortality they cause via cerebral infarction, but also because of their role in the causation of mycotic aneurysms, brain abscesses, and abnormal CSF formulae. (3) Cerebral emboli are particularly common in patients with mitral valve infection, and in patients with infection due to virulent organisms, particularly S. aureus and enteric gram-negative bacilli. (4) Mycotic aneurysms occur more frequently in the course of acute endocarditis rather than late in the course of subacute disease. Management of angiographically demonstrated mycotic aneurysms is dependent upon the presence or absence of hemorrhage, the anatomic location of the aneurysm, and the clinical course of the patient. Healing of mycotic aneurysms can occur during the course of effective antimicrobial therapy, thus obviating the need for neurosurgical intervention in all such patients. (5) Macroscopic brain abscess is a rare complication of bacterial endocarditis. Miliary microscopic abscesses are more common than larger abscesses, particularly in patients with acute disease and miliary infection in other organs of the body. (6) Focal seizures occur most commonly in endocarditis patients with acute embolic disease; generalized seizures are of diverse etiologies, with metabolic factors being most important. Penicillin neurotoxicity should be considered in patients with impaired renal function who are receiving high dose penicillin. (7) With the exception of hemorrhagic complications, lumbar puncture results tend to reflect the nature of the infecting organism rather than the nature of the neurologic complication. Endocarditis due to virulent organisms such as S. aureus is usually associated with a purulent CSF formula while nonvirulent organisms, such as viridans streptococci, susually have aseptic or normal CSF formulae.