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Aim: To determine the prognostic value of conventional electroencephalography (EEG) monitoring in neonatal hypoxic–ischemic encephalopathy (HIE). Method: In this multicentre retrospective study, 95 full‐term neonates (mean of 39.3wks gestational age [SD 1.4], 36 [38%] females, 59 [62%] males) with HIE (2013–2016) undergoing therapeutic hypothermia were divided between favourable or adverse outcomes. Background EEG activity (French classification scale: 0–1–2‐3‐4‐5) and epileptic seizure burden (epileptic seizure scale: 0–1‐2) were graded for seven 6‐hour periods. Conventional EEG monitoring was investigated by principal component analysis (PCA), with clustering methods to extract prognostic biomarkers of development at 2 years and infant death. Results: Eighty‐one per cent of infants with an adverse outcome had a French classification scale equal to or greater than 3 after H48 (100% at H6–12). The H6–12 epileptic seizure scale was equal to or greater than 1 for 39%, increased to 52% at H30–36 and then remained equal to or greater than 1 for 39% after H48. Forty‐five per cent of infants with a favourable outcome had a H6–12 French classification scale equal to or greater than 3, which dropped to 5% after H48; 13% had a H6–12 epileptic seizure scale equal to or greater than 1 but no seizures after H48. Clustering methods based on PCA showed the high efficiency (96%) of conventional EEG monitoring for outcome prediction and allowed the definition of three prognostic EEG biomarkers: H6–78 French classification scale mean, H6–78 French classification scale slope, and H30–78 epileptic seizure scale mean. Interpretation: Early lability and recovery of physiological features is prognostic of a favourable outcome. Seizure onset from the second day should also be considered to accurately predict neurodevelopment in HIE and support the importance of conventional EEG monitoring in HIE in infants cooled with therapeutic hypothermia. What this paper adds: Comprehensive analysis showed the high prognostic efficiency (96%) of conventional electroencephalography (EEG) monitoring.Prognostic EEG biomarkers consist of the grade of background EEG activity, its evolution, and the mean seizure burden.Persistent seizures (H48) without an improvement in background EEG activity were consistently associated with an adverse outcome. [ABSTRACT FROM AUTHOR]