In contrast, osteosclerosis, a very uncommon entity in the general population, is defined as the increase of bone mass. In general, it is due to a defect in bone resorption. It may accompany a variety of bone disorders such as renal osteodystrophy, Paget´s disease, or oxalosis, among others. In uremic patients, osteosclerosis appears more commonly in the axial skeleton, associated with secondary hyperparathyroidism. In these cases, increased bone density is found in the upper and lower extremes of the vertebrae, producing the well known “rugby jersey” image. The physiopathology of osteosclerosis is not well known.