The task of the legal psychiatric expert is to establish whether the accused was suffering from insanity or some form of mental abnormality when the offense was committed and to advise the court on the need for psychiatric placement of the offender. To this end, a thorough biological and psychiatric examination of the offender using uniform scientific techniques is essential. To employ electroencephalography as an effective part of such an examination, experts must interpret electroencephalograms (EEG'S) within the context of other findings without expecting the EEG's themselves to be definitive. Furthermore, EEG's must be evaluated through collaboration of legal, medical, and social experts. For medicolegal purposes, EEG's may be useful in civil cases to assess the extent of cranial trauma, especially when the EEG's are repeated over a period of several months. In criminal cases, epilepsy determination proves particularly problematic, as experts must be able to ascertain whether the offender was actually under the influence of the illness when he committed a crime. In general, EEG findings will either be normal, indicate a disturbance of mental function in a known mental patient without establishing whether the anomaly is the cause of the mental disorder, or show anomalies in subjects thought to be normal. Criminologists have attempted to relate certain EEG patterns to delinquency. A high frequency of theta rhythms occurs among adult delinquents, a characteristic usually present at such frequencies in children and adolescents. Theta rhythms may result from an organic brain disturbance (low frequency, from 4 to 6 pulses per second), neurotic conditions (6 to 7 pulses per second), or from the conditions of the examination. Low frequency alpha rhythms have been associated with delinquency and with alcoholism. It is stressed that EEG's are especially difficult to read because values of the criteria for analysis (e.g., frequency, voltage, and morphology) are only approximate. Conclusions reached through study of groups form the basis for interpretation. --in French.