Osteopetrosis (marble bones, Marmorknochenkrankheit, Al bers\x=req-\ Sch\l=o"\nberg'sdisease, osteosclerosis fragilis generalisata, maladie des os marmor\l=e'\ens) is a disease characterized essentially by increased thickness and density of the cortical and spongy portions of the entire osseous system. The marrow cavity may be encroached on to the point of obliteration, and there are frequent but less constant alterations in the external configuration of certain parts of the skeleton. Roentgenographically the individual bones appear opaque, heavy and lacking in finer structure. These changes are characteristically, although not invariably, associated with a myelophthisic type of anemia, the origin of which is closely bound up with the etiology of the osseous sclerosis. There may be other manifestations, such as multiple pathologic fractures, chronic osteomyelitis, hydrocephalus, optic atrophy and enlargement of the liver, the spleen and the lymph nodes throughout the body. The disease shows a striking familial tendency and is occasionally hereditary.Osteopetrosis is a rare disease. Sixty-five cases have been reported in the literature, either in detail or by allusion, up to 1932. To this number may be added the case which we are about to describe. The condition deserves the attention of pediatricians. In fully half the pub¬ lished reports the diagnosis was made before the twelfth year of life, and it may be assumed that in many of the remaining patients the dis¬ ease developed well within the pediatric age period. Notwithstanding this fact we have been unable to discover a discussion of osteopetrosis in English in a pediatric journal. Numerous reports of cases and critical dissertations have appeared in German, but the only easily avail¬ able articles in English are those of