Background. Evaluation of the severity of brain damage in newborns with hypoxic-ischemic encephalopathy (HIE) may be difficult with the use of sedation and a delay in hospitalization. Objective. The aim of the study was to evaluate the diagnostic and prognostic value of amplitude-integrated electroencephalography (aEEG) in the application of sedation in newborns at the age of 24 hours of life. Methods.The study was conducted among 50 newborns with HIE of varying severity. aEEG was used for newborns at the age of 24 hours of life. The experimental group included 28 newborns with pathological aEEG models at the age of 24 hours of life. The control group included 22 newborns aged 24 hours of life with a normal aEEG pattern. We compared neurological, laboratory, morphological data, as well as the outcome of the disease. The value of aEEG in predicting the neurological outcome was evaluated. Results. In the experimental group, bradycardia after birth, metabolic acidosis at admission, CNS depression, convulsive syndrome, application of anticonvulsants, cerebral edema in the early days of life were more often observed. Also in the experimental group, longer duration of mechanical ventilation, longer hospital and intensive care unit length of stay were observed. Infants in the experimental group were more likely to have convulsive syndrome, bulbar disorders and atrophic brain damage. AEEG recorded at the age of 24 hours of life had a sensitivity of 87%, a specificity of 70%, a positive predictive value of 71% and a negative predictive value of 86%. The positive likelihood ratio at the age of 24, 36 and 48 hours of life was 2.9, 3.1 and 7.6, respectively. Conclusion. In newborns with HIE pathological patterns of aEEG in first 24 hours of life are associated with a more severe brain damage and an adverse neurological outcome. The greatest positive likelihood ratio is observed at the age of 48 hours of life. Probably, the depth of depression of electrocortical activity during sedation depends on the severity of the CNS lesion.