Objective To examine nitric oxide (NO) and nitric oxide synthase (NOS) concentrations in serum and cerebrospinal fluid (CSF) of children with epilepsy (EP) or febrile convulsions (FC) and to investigate the role of NO in the pathogenesis of EP and FC. Methods The serum and CSF concentrations of NO and NOS in children with EP (EP group, n=31) or FC (FC group, n=39) were examined by nitrate reductase and enzyme determination assays respectively within 24 hours after seizures. The results were compared with 38 control children with upper respiratory infection. Results Both EP and FC groups demonstrated a lower CSF NO levels compared with the Control group (P< 0.05). In contrast, serum NO levels in both groups were significantly higher than those in the Control group (P< 0.05). CSF levels of NOS in the FC group decreased significantly when compared with the Control group (P< 0.05). Conclusions CSF NO levels decreased after seizures in children with either EP or FC. CSF levels of NOS also decreased in the FC children. The results indicate a possible role of NO in anti-convulsion.