Periodontosis is an idiopathic degeneration of the periodontium which results in migration and loss of teeth. The disease begins in the regions of the incisors and first molars. Late in the disease, other areas of the dental arches may be involved. The gingivae are not initially inflamed, and there are no associated systemic abnormalities. Local irritants cannot account for the marked alveolar destruction which leads to the tooth loss. Several heritable syndromes and periodontitis also may be associated with alveolar bone destruction. Periodontosis can be differentiated each of these on the basis of negative laboratory tests, lack of associated anomalies, distinctive pattern of bone loss and timing of onset of gingival inflammation. A family in which periodontosis was present in three of six sibs and in which ichthyosis was segregating independently of periodontosis is reported.