The karyotype of the Brazilian lizardPolychrus spshowed 2n=20 chromosomes for the female and 2n=19 chromosomes for the male. The meiotic cells of the male in diakinesis and metaphase I showed 8 bivalents and 1 trivalent. In metaphase II there were cells withn=9 chromosomes, and cells withn= 10 chromosomes. The sex determining mechanism was interpreted as belonging to the « pseudo XO/XX » type, which differs from the X1X2Y/X1X1X2X2type because the Y is morphologically indistinguishable from the X2chromosome. This is the second occurrence of this case to be described in the vertebrates.