The value of long-term EEG recordings for diagnosis and differential diagnosis of epilepsy is described. It is emphasized that long-term EEF monitoring increases the scope of EEG techniques and improves the diagnostic value of standard EEG recordings providing up to 90% positive diagnostic information. In particular, the value of ambulatory cassette recording is stressed. Allowing quantification of epileptic activity recorded in real-life situation, useful information not available by means of standard EEG recordings can be obtained. Recording and scoring all-night sleep, it enables studying abnormalities of sleep patterns. In addition the value of long-term EEG recordings in therapy and control of epileptic patients is pointed out and discussed.