Humerus varus, the upper extremity analogue of coxa vara, may be found in association with, and probably as a consequence of hematologic, infectious metabolic, genetic and neurologic disorders. No matter what the etiology, there is a similar pattern of development and progression of the deformity. The medial region of the proximal humeral physis either develops slowly or failed to develop, while the lateral region develops more rapidly, causing varus rotation of the proximal humeral epiphysis and physis. In the more extreme cases, the lateral region of the growth plate is almost parallel to the longitudinal axis of the shaft. In many cases there is a medial lucency, adjacent bony epiphyseodesis, and significant shortening of the humerus. Although abduction is usually decreased, major functional impairment is unusual even in the dominant arm.