We report a 72-year-old male patient with a 47,XYY/45,X/46,XY mosaicism associated with short stature, exostoses, type E brachydactyly, gynecomastia, cryptorchidism, mild mental retardation, and a paranoid personality and conversion disorder. Since his prevalent cell line was 47,XYY (about 75%), our patient could be karyotypically classified as a case of 47,XYY syndrome. In view of the striking similarity of the clinical features of this case and those of a XYY case previously reported by Ikegawa et al (1992), it seems reasonable to suggest that these patients are representatives of a novel syndrome with a XYY karyotype.