Childhood absence epilepsy (CAE) is a relatively rare form of idiopathic generalized epilepsy, occurring in previously normal children with a strong genetic predisposition. The annual incidence of CAE has been estimated at 6.3/100,000 to 8/100,000 children aged 0-15 years.Medical and electroencephalographic records of 50 Chinese children with CAE were reviewed.There were 22 males and 28 females. The age of onset ranged from 3 to 12 years with a mean of 6.9 +/- 2.4 years. Six children (12%) had positive familial epileptic history and 11 patients (22%) had a past history of febrile convulsion. Electroencephalographically, there were posterior delta rhythm (6/50), frontocentral (1/50), and centrotemporal (1/50) spikes in addition to the characteristic 3 Hz spike and wave complex. All patients received regular or irregular treatment with valproate. Sixteen patients (32%) evolved to generalized tonic-clonic seizure (GTCS) with a mean of 2.1 +/- 1.6 years of lag from stopping valproate. The patients with GTCS had significant late onset of age, a longer active period, and longer treatment duration than those without GTCS (p < 0.01). There were significantly more patients with irregular treatment evolving to GTCS than those with regular treatment (p < 0.01). None of the patients with posterior delta rhythm evolved to GTCS.Regular treatment with valproate is the modality of choice in the management of CAE. Posterior delta rhythm seems to be a good prognostic factor electroencephalographically.