Cytogenetic studies on a 17-year-old phenotypic male, with short stature and clinical and hormonal features of hypogonadism similar to those of an XX male, revealed an X;Y translocation, karyotype, 46,Xt(X;Y)(p22;?p11?q11). He was H-Y antigen positive. X inactivation studies showed inactivation of the abnormal X in the majority of cells (60 to 70%) and inactivation of the normal X in the remaining cells. Gene marker studies, including Xg blood grouping, showed no anomalous segregation. This patient is the second reported male showing a positively identified X;Y tanslocation with no detectable free Y chromosome and provides further indirect evidence for an X-Y interchange in the aetiology of XX male sex reversal.