BACKGROUND: Semiology of epileptic seizure is very important for diagnosis and treatment. However, little is known about the reliability of the observers' description. This study aims to determine the description reliability of seizures in the aspects of classification and lateralization. METHODS: We recorded 72 patients with habitual seizures during video-EEG monitorings. We, then, compared the ictal behaviors described by frequency observers and those recorded on the videotape to compare the accuracy of the observers' descriptions. Finally, we reviewed which aspects of the informants affected the reliability of the data. RESULTS: The classification of seizures based only on the observer-description was somewhat discordant from the videotape (correct classification: 82%) especially in dividing simple partial from complex partial seizures. Description of many ictal behaviors in presumed complex partial seizure such as oroalimentary automatism, motionless staring, tonic/clonic posture and version was accurate except for the hand automatism. A specified direction by the observer has a very high true positive rate. The accuracy of the description was related to the educational status of the observer. CONCLUSIONS: Semiology description by well-educated observers is may be reliable, but every physician should keep its limitation in mind and judge accordingly.