The clinical study of this case forces us to amend the current conception of the cause of an angular kyphos. A kyphos is not necessarily produced by a change in the shape of the vertebral bodies. It may also be caused by an inflammatory lesion of the bone, which, without resulting in actual bone destruction, seems to favor a softening of the intervertebral discs and a consequent deviation of the spinal bodies frcm the normal alignment. In the lumbar region the kyphosis could be produced by a spasm of the psoas muscle, which, taking its origin from the lateral process, would cause a buckling of the spine demonstrable in the roentgenogram by a narrowing of the anterior portion of the intervertebral spaces. In the case studied, the inflammatory lesion was due to the streptococcus viridans, which in this, as well as in other reported cases, causes bone inflammation without pus formation.