Five new cases are added to the single published instance of Yq to Xp translocation(Xt) in man. It is shown that the anomaly can occur as a mutational event during meiosis, and can be inherited from a parent, but also that it can arise in a 47,XXY embryo. In individuals with 46,XXt karyotype the gonadal development, sexual differentiation, gonadal function and fertility are within the range of normal females. They do not present overt or discrete signs of virilisation. However, somatic stigmata, and more specifically short stature, are present in all patients. There is no uniform pattern of Xt inactivation which varies from random to apparently preferential inactivation. This phenomenon may be important for the better understanding of X-inactivation which for the Xt the authors believe is random but followed by differential proliferation of the resulting two types of cells.