To approach the problem concerning whether or not anti-epileptic treatment of benign childhood epilepsy with centro-temporal spikes (BCECT) is necessary, we retrospectively studied 6 untreated and 39 treated patients with BCECT and compared their clinical findings after 2 years of observation. Then we selected 6 untreated and 28 treated patients from the same series who had been free from attacks for more than 2 years to determine whether the mode of onset (multiple seizures or isolated one for the first month of the illness) was related to the duration of active epilepsy in these two groups. This comparative study of untreated and treated patients followed for 2 years revealed no differences in the interval between first visit and start of attack-free period between the two groups. The mean duration of active epilepsy in those with only isolated seizures at onset was significantly shorter than that in those with multiple seizures at onset. Anti-epileptic medication may be unnecessary in patients with isolated seizure during sleep; it does not affect the natural course of BCECT. Treatment is necessary for a longer period in patients with multiple seizures at onset than in those with isolated seizures at onset.