A Polled Hereford bull with good libido displayed gross testicular hypoplasia and azoospermia. His left testis weighed 23.6 g, approximately 10% of the testis weight of normal Herefords. Histopathologic examination of the left testis revealed small seminiferous tubules in advanced degeneration and very few with Sertoli cells. The number of Leydig cells was disproportionately large in relation to the seminiferous tubules. From both leucocyte and tissue cultures, the karyotypes were 61, XXY. This bull represents the bovine counterpart of human Klinefelter's syndrome.