The carrying angle is said to be greater in the XO phenotype than in XX and greater in XX than in XY. To determine the effects of the sex chromosomes on the carrying angle, the angles of chromosomally normal and abnormal patients were compared. Among women, only XO phenotypes did not differ substantially from XX. Among men, all comparisons showed a considerable difference, with the difference between XY and XYY phenotypes being highly significant. In sex chromosome aneuploidy, there appears to be a spectrum of elbow abnormalities with maximal cubitus valgus in XO phenotypes at one extreme, decreasing degrees of valgus in XX and XY, and approaching cubitus rectus in cases with one supernumerary X or Y, with cubitus varus and radioulnar synostosis and radial head dislocation where there are multiple supernumerary sex chromosomes. (JAMA 230:718-720, 1974)