Increased serum level of malondialdehyde (sMDA) in neonates with hypoxic-ischaemic encephalopathy (HIE) was evaluated as a possible criterion for determining HIE severity. Mean body weight and gestational age in a healthy control group of neonates (n = 63) and in neonates with HIE (n = 69) were statistically similar. Apgar scores at 1 and 5 min for the HIE group were significantly lower than for the control group. The mean sMDA level for the HIE group was significantly higher than the control group. Within the HIE group, the sMDA level for neonates with Sarnat's grade II and III was significantly higher than for those with Sarnat's grade I. There was a significant correlation between Sarnat's grading and the sMDA level. The sMDA level was significantly higher for neonates who died (n = 20) compared with those who survived (n = 49). In conclusion, the sMDA level was highest in neonates with HIE and correlated with HIE severity. The sMDA concentration could, therefore, be used as a criterion for predicting disease severity.