OBJECTIVE: To examine electroencephalographic (EEG) background patterns and serum neuron specific enolase (NSE) levels in neonates with hypoxic-ischemic encephalopathy (HIE) in order to study their roles in assessing clinical progress, severity and prognosis in children with HIE. METHODS: A total of 58 neonates with HIE, including 38 cases of mild, 12 cases of moderate and 8 cases of severe HIE, were enrolled. Thirty normal neonates were used as the control group. Serum NES levels were measured by radioimmunoassay 12-24 hrs and 7-10 days after birth. EEG examination was performed 24 hrs-18 days of age (early stage) and 28-30 days of age (convalescence stage). The neonates with HIE were followed-up, with a duration of 6 months to 3 years. RESULTS: Fifty-five neonates with HIE (94.8%) showed EEG abnormalities in the early stage, but only 2 patients (6.7%) in the control group (P<0.01). EEG background patterns abnormalities in the early stage were found in 90.0% (18/20) of moderate-severe HIE neonates. The proportion was significantly higher than that in the mild HIE group ［5.2% (2/38); P<0.01］. Thirteen (72.2%) out of 18 patients with early EEG background patterns abnormalities had poor outcomes. Serum levels of NES in the HIE group were significantly higher than those in the control group 12-24 hrs after birth (P<0.01). EEG background patterns abnormalities and increased serum levels of NES 12-24 hrs after birth were consistent with the clinical grading of HIE. Most of neonates ［87.5% (7/8)］ who showed abnormal EEG background patterns at the convalescence stage had neurological sequelae. CONCLUSIONS: EEG background patterns and serum NSE levels may be useful in assessment of disease severity and neurological outcome in children with HIE.［Chin J Contemp Pediatr, 2009, 11 (3):173-176］