Seventy-three seizures in 18 epilepsy patients were studied by analyzing the ictal findings of 8-channel ambulatory EEG (A/EEG) and adjacent 16-channel intensive videomonitoring (IVM). With IVM and A/EEG analysis, accuracy was excellent for determining the lateralization of seizure progression; whereas at seizure onset and post-ictal slowing, accuracy was poor. No false lateralization was found in A/EEG compared with IVM or lateralization according to patient data, and in seizure lateralization the interpretation of A/EEG was discordant in only 3 seizures with IVM analysis. According to our study, ictal 8-channel A/EEG with sphenoidal electrodes is not suitable for localization of temporal lobe foci, but is reliable for lateralization analysis.