Variously known also as encephalopathy and delirium, confusion in patients presents diagnostic and management challenges to physicians in the emergency room, the hospital wards and the intensive care units. There have been few tools to diagnose and follow the treatment of encephalopathic patients, and clinicians increasingly are aware of the supplemental information that EEG can offer beyond clinical examination and cerebral imaging. The EEG reveals a variety of patterns typical of encephalopathy that represent the severity of cerebral compromise, the presence of ictal complications, and a rough guide to the relative contributions of several concurrent causes of impaired consciousness. These EEG patterns may correspond to different levels of consciousness, stages of evolution, etiologies and potential reversibility. Studies have revealed the significance of triphasic waves, slow delta activity, mixed theta/delta, and frontal intermittent delta and their clinical associations with structural, infectious, toxic or metabolic problems, and outcome. Correlations can be made among EEG and imaging studies to help the intensivist and clinician produce a more comprehensive picture of the delirious patient. Along with the clinical examination and complementary studies, the management team can then be guided towards optimal management strategies of these critically ill patients.