Pathologic examination of sternums from young growing rats revealed a number of skeletal lesions involving both cartilage and bone elements. Degeneration or aseptic necrosis of the intersternebral cartilage was a frequent finding in most rats that were examined either at 130 or 180 days of age. Thickening of the sternal cortices and trabeculae containing prominent cement lines were less frequently occurring lesions in these sternums. These changes were absent in rats of 70 days of age. The etiology of the lesions is not understood, although several factors may be incriminated.