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The basic approach to an encephalopathic EEG consists of diagnosing encephalopathy, estimating its severity, identifying repetitive patterns and NCSE, if present. The three cardinal electrographic features of encephalopathy include background slowing, amplitude attenuation/suppression and loss of reactivity. Severe encephalopathies are typically characterized by a low amplitude, slow and unreactive record, while a reversal of these trends may indicate improvement. Estimation of severity differs from prognostication. Repetitive patterns (rhythmic and periodic) are common in encephalopathic patients and have important implications regarding etiology, epileptogenicity and prognosis. NCSE results from electrographic ictal activity that contributes to the encephalopathic state. It should be diagnosed based on clinical signs, EEG findings and a response to antiepileptic medications. NCSE is independently associated with increased mortality. Spindle coma is characterized by slow background with frequent symmetric spindles, typically has a favorable prognosis in those with reactivity and without evidence of structural damage. Alpha coma consists of unreactive alpha frequencies, they have a posterior predominance in brainstem lesions and an anterior or diffuse distribution with cerebral anoxia. Posterior predominant alpha coma should be differentiated from a locked-in syndrome. Beta coma typically occurs from drug overdose and usually has a favorable prognosis. CJD and SSPE are infectious encephalopathies with distinct electrographic presentations that typically consists of GPDs. Extreme delta brush pattern commonly occurs in Anti-NMDA receptor encephalitis.