Introduction. In El Salvador, encephalopathy is one of the clinical conditions with the greatest uncertainty when assessing the prognosis of a patient in the intensive care unit. The electroencephalogram offers a low cost, practical, non-invasive and highly available method through which an evaluation of the neurological status of the patient is achieved. Objective. Study was carried out with the aim of correlating electroencephalographic patterns and clinical evolution of patients with encephalopathy admitted to the medical and surgical intensive care unit during the months of September to December 2018, in National Hospital Rosales. Methodology. An observational, descriptive, longitudinal, prospective. Results. Patients with a diagnosis of encephalopathy were included and chronicled clinical and electroencephalographic variables,age, sex, comorbidities, cause of admission to the intensive care unit, medical or surgical, use of sedative or relaxing drugs, use of vasoactive amines, state of consciousness, complications during intrahospital stay, evolution and outcome: death, transfer or discharge. Conclusion: The most common pattern among patients was epileptiform, showing the highest degree of survival among them, when treated with antiepileptic drugs. The reactivity showed a prognostic value among the patients, 44.44% of 9 non-reactive patients died, and while the 6 reactive patients showed a 100% survival of patients with encephalopathy and EEG pattern with reactivity present during the period of time admitted.