We reviewed the records of 20 patients with late prosthetic valve endocarditis who were hospitalized at the University of Iowa between 1985 and 1988. There were 14 men and six women, aged 20-80 (mean 57.9) years. The infected valves were mechanical in 11 patients (six aortic and five mitral) and bioprosthetic in the other nine. Echocardiography in 12 patients demonstrated vegetations in one. Among the 20 patients, neurologic complications occurred in eight (40%), six of whom had mechanical valves (five mitral and one aortic). Infection with Staphylococcus aureus occurred in four of the eight patients (50%) with neurologic complications. Of the eight patients with neurologic complications, ischemic stroke was diagnosed in four, transient ischemic attacks in one, and intracranial hemorrhage in three. Prothrombin times at the time of the intracranial hemorrhage were 2.2, 1.5, and 1.3 times control in these three patients. Cerebral angiography done in four of the eight patients with neurologic complications failed to show mycotic aneurysms. Nine of the 20 patients (seven men and two women, mean age 66.8 years) died less than or equal to 90 days after the diagnosis of late prosthetic valve endocarditis. Half of the eight patients with neurologic complications died (three men and one woman, mean age 62.3 years), and all three patients with intracranial hemorrhage died. Our data suggest that the neurologic complications of late prosthetic valve endocarditis are more common with mechanical valves, particularly in the mitral position, and are associated with a high mortality.