Six additional cases of infantile cortical hyperostoses are described. Ten cases have now been reported from this clinic. The findings indicate that this disorder is a new infantile syndrome for which the cause is unknown and the pathogenesis obscure.

The skeletal lesion is a hyperplasia of subperiosteal bone on the peripheryof the cortex. Pleural exudate removed from one patient contained 500 monocytes per cubic millimeter. The nature of the soft tissue swellings and the tissue elements in them which are affected primarily have not been determined.

The components of the syndrome common to all patients are deep swellings of the soft tissues and cortical hyperostoses in the neighboring bones. Other important features lacking in some patients include fever, hyperirritability, pseudoparalysis, dysphagia, pleurisy, anemia, leucocytosis, monocytosis, increased rate of sedimentation of erythrocytes, and excessive serum phosphatase. Soft tissue swellings have been located in the scalp, face, neck, thorax, and extremities. Hyperostoses have been demonstrated in the calvarium, mandible, clavicles, scapulas, ribs and the tubular bones of the extremities including the metatarsals. The mandible and the clavicles are affected most frequently.

Initial symptoms have appeared as early as the third week of life andas late as the twentieth month. Duration of the active manifestations has varied from eight weeks to nine months. All patients have recovered. The course of the disease has not been modified by the administration of sulfonamides or penicillin.