The persistent Müllerian duct syndrome is characterized by the retention of Müllerian derivatives in patients otherwise normally virilized. Clinically, the persistence of uterus and tubes leads either to cryptorchidism or inguinal hernia, depending on whether or not the Müllerian derivatives can be mobilized during testicular descent. The condition is usually discovered at surgery, however preoperative sonography could allow the diagnosis to be made preoperatively. The molecular basis of the persistent Müllerian duct syndrome is heterogeneous, and is reflected by wide variations in the serum concentration of anti-Müllerian hormone. Some cases are apparently due to end-organ resistance, and are associated with normal serum levels of the hormone. Others, characterized by absent or low hormone concentrations, can be explained by mutations of the gene coding for anti-Müllerian hormone, which are distributed along the whole length of the coding region.