Since the tentative establishment of a fairly high incidence of sex chromosome aberrations among offenders institutionalized in prison psychiatric wards, a certain number of facts have been established. First, a long Y-chromosome is not irrevocably linked to delinquency. The long Y-chromosome occurs frequently among Asiatic and Semitic populations without a corresponding increase in crime rates. An excess of X-chromosomes has the same effect as an excess of Y-chromosomes. Y-chromosome anomalies are often found in families with environments conducive to delinquency, so it is difficult to ascertain whether genes or environment is responsible for criminal behavior. Delinquents with 47,XYY karyotypes display the same characteristics as psychopaths, e.g., aggressiveness, low frustration levels, and egocentricity. The frequency of 47,XYY subjects is especially high among mentally ill individuals, whether delinquent or not (10 to 20 times higher than among the normal population). Abnormal behavior is probably due more to disequilibrium of the gene formula than to a specific gene. Unfortunately, media popularization of scientific hypotheses has created the myth of the 'chromosome of crime.' It is uncertain whether or not informing parents of infants' gonosome abnormalities would negatively influence their attitude towards their child. The author recommends that individuals with sex chromosome anomalies be considered competent to stand trial. Deviant behavior in such individuals is attributed to their mental illness rather than to their chromosome anomalies. A 19-item bibliography and the text of a discussion about the paper are supplied.--in French.