The clinical features of 42 patients with the only recently recognized and generally fatal neurological syndrome of progressive dialysis encephalopathy are reviewed and the electroencephalographic and neuropathological findings are summarized. Despite apparently successful hemodialysis, these patients develop a wide spectrum of neurological abnormalities. Of these, sudden onset of hesitant, nonfluent speech is the most characteristic and usually the earliest sign. Both dysphasic and dysarthritic elements are found, though the former predominate. Myoclonus, dementia, seizures, and gait difficulty are also seen in the majority of these patients. EEGs are more abnormal than would be expected for the clinical severity, with some type of high-voltage spike-wave pattern intermixed with abundant slow activity. The combination of clinical and EEG features in the appropriate setting is virtually diagnostic. Transient episodes with variable periods of complete or partial remission have been recognized. Neuropathological changes are surprisingly mild and nonspecific. The cause is uncertain; current speculation focuses on aluminum as the offending neurotoxin. Treatment remains unsatisfactory.