To define the EEG and associated clinical features of septic encephalopathy, we studied 62 patients with positive blood cultures. Patients were divided into three clinical groups: nonencephalopathic (NE), mildly encephalopathic (ME), and severely encephalopathic (SE); the latter two groups had diffuse cerebral dysfunction. EEGs were classified into five groups: normal, excessive theta, predominant delta, triphasic waves, and suppression or burst suppression, in ascending order of severity. The EEG (1) was more sensitive than our clinical criteria for encephalopathy, (2) showed features that were, when considered with clinical and laboratory characteristics, compatible with a potentially reversible encephalopathy, and (3) had well-defined categories that correlated with percent mortality, even within a single clinical group. We conclude that the EEG is a sensitive index of brain function in septic encephalopathy and that it is especially useful in the intensive care monitoring of patients with sepsis.