Sixty-four children, aged 0-17 years, undergoing ambulatory electroencephalography (EEG) were prospectively recruited during a 12-month period. The diagnostic yield of ambulatory electroencephalography was determined for each of the following groups: group 1: differentiation of seizures from nonepileptic events; group 2: determination of seizure/interictal discharge frequency; and group 3: classification of seizure type or localization. The ambulatory electroencephalography answered the clinical question in 61% of group 1 (27/44) and 100% of groups 2 (16/16) and 3 (4/4). Of 44 cases in Group 1, clinical events were recorded in 61%; the ambulatory electroencephalography result changed the diagnosis from epileptic to nonepileptic or vice versa in 27%. When clinicians suspected that events were epileptic, ambulatory electroencephalography changed the clinical impression in 50%, whereas when events were suspected to be nonepileptic, ambulatory electroencephalography confirmed that impression in 83%.