Sex chromosome anomalies are frequently expressed as malformations of the reproductive organs and constitute sporadic birth defects in domestic animals, which often leads to infertility. In the presence of a normal karyotype, abnormalities in the genital tract development can occur. Intersex condition is relatively frequent in goats and pigs, but less frequent in sheep and dogs. In ruminants, most intersexes conditions correspond to XX/XY haematopioetic chimaeras and fit in the freemartinism syndrome. However, sporadically cases of male pseudohermaphroditism are reported that can be differentiated from the freemartinism syndrome through the karyotype as well as by the morphological characteristics of the genital tract. These are XY animals that evidence a variable differentiation of the genital tract, owing to varying degrees of the external genitalia and paramesonephric ducts associated with inadequate production of testosterone or Anti-Müllerian Hormone by the fetal testes. Male pseudohermaphroditism may occur in distinct varieties. Male pseudohermaphroditism includes male to female sex reversal a condition where, consecutive to a disrupted gonadal differentiation or to an abnormal development of the Leydig cells, testosterone production is impaired; this syndrome may present distinct clinical gradations, whether a streak gonad or a dysgenesic gonad develops. Total absence of androgens induces feminization of the reproductive tract, while impaired testosterone production and accumulation of testosterone precursors may originate ambiguous genitalia. In the androgen insensitivity syndrome, another form of male pseudohermaphroditism also called the testicular feminization syndrome, despite the presence of testes and a XY karyotype, almost normal-appearing female phenotypes can be found. This condition is associated to a defect in the androgen receptor mechanism that leads to a resistance to the testosterone action at the cellular level in the external genitalia embryonic rudiments. Frequently, animals usually are XY individuals evidencing female like or ambiguous external genitalia. Persistency of the Müllerian ducts is another male pseudohermaphroditism condition, associated with the inadequate production of anti-müllerian hormone or to the absence of its receptors, which can reveal female or ambiguous external genitalia. A steroid 5α-reductase deficiency, impairing dihydrotestosterone formation, might also be responsible for male pseudohermaphroditism. Based on three distinct forms of male pseudohermaphroditism recently evaluated by our Clinical Services, the aims of this study includes the morphological, histological and immunohistochemical description of this condition in normal XY karyotype males (in both blood and fibroblast samples), and the discussion of the cases through a review of the literature, in order to improve our 5 knowledge of male pseudohermaphroditism.