The purpose of this report is not to describe a new condition but to remind those who seldom see smallpox of one of its most important and easily recognised complications. Bone infection can be late, almost silent and often most unexpected. It is usually symmetrical and almost always multiple. It does not affect the spine, pelvis and ribs, but does affect the arms, hands, legs and feet. It is destructive, unpreventable and untreatable. It ends with deformity but not with loss of life. The recognition of its etiology will prevent a great deal of unnecessary and unrewarding interference with a self-limiting disease.