AMONG THE SUBJECTS STUDIED WERE THREE PATIENTS REFERRED TO PSYCHIATRIC HOSPITALS FOR ANTISOCIAL AND AGGRESSIVE BEHAVIOR AND ONE PATIENT REFERRED FOR CHROMOSOME EXAMINATION BY A DERMATOLOGY CLINIC WHERE HE HAD BEEN ADMITTED FOR HYPOGONADISM. A NUMBER OF CHARACTERISTICS TENATIVELY LINKED TO THE XYY SYNDROME INCLUDE ACCELERATED GROWTH, GENITAL MALFORMATIONS, SKELETAL ABNORMALITIES, DELAY OF PSYCHOMOTOR DEVELOPMENT, AND UNSTABLE BEHAVIOR WITH AGGRESSIVE REACTIVITY. EXAMINATION OF THE FOUR STUDY SUBJECTS REVEALED THAT TWO OF THE PATIENTS HAVE A SINGULAR XYY KARYOTYPE AND DO POSSESS SOME OF THE FEATURES ATTRIBUTED TO THE XYY SYNDROME, ONE PATIENT HAS A CHROMOSOMIC MOSAIC, AND THE OTHER PATIENT HAS A NORMAL CHROMOSOME. RESEARCHERS CONCLUDED THAT EPIDEMIOLOGIC RESEARCHES IN THE XYY SYNDROME ARE STILL INSUFFICIENT FOR THE FOLLOWING REASONS: (1) NONUNIVERSAL SAMPLES WERE USED; (2) THE LARGE NUMBER OF HEREDITARY DISEASES AND THE VARIETY OF THEIR CLINICAL FORMS CALLS FOR MULTIDISCIPLINARY RESEARCH ON DEVIANT PERSONALITIES, WITH PSYCHIATRISTS GIVING SPECIAL ATTENTION TO XYY PATIENTS; (3) BECAUSE SYMPTOMS OF THE XYY SNYDROME VARY SO GREATLY, THE IDENTIFICATION OF THE SYNDROME WITH PSYCHOPATHOLOGICAL OR CRIMINAL SYNDROMES SHOULD BE ABANDONED; AND (4) IMPROVEMENT IN PSYCHIATRIC TREATMENT DEPENDS ON CONTINUED RESEARCH ON DEVIANT PERSONALITIES WITH RESPECT TO PRENATAL INFLUENCES AND RELATED ENVIRONMENTAL FACTORS. SUMMARIES OF CONCLUSIONS ARE PRESENTED IN FRENCH, GERMAN, DUTCH, ITALIAN, AND SPANISH AS WELL AS ENGLISH. REFERENCES AND STUDY ILLUSTRATIONS ARE PROVIDED. (DAG)