Autosomal recessive “malignant” osteopetrosis is a rare congenital disorder of bone resorption. It is caused by the failure of osteoclasts to resorb immature bone.1-3 This leads to abnormal bone marrow cavity formation and clinically to the signs and symptoms of bone marrow failure. Impaired bone remodelling causes bony narrowing of the cranial nerve foramina which results in cranial nerve, especially optic nerve, compression.2Pathologically there is a persistence of the primary spongiosa characterised by cores of calcified cartilage within bone. Abnormal remodelling of primary, woven bone to lamellar bone results in “brittle” bone that is prone to fracture.1 ,2 Thus fractures, visual impairment, and bone marrow failure are the classical feature of the disease.4 Osteopetrosis has been reported in most ethnic groups although as the disease is very rare it is more frequently seen in ethnic groups where consanguinity is common. Infantile onset osteopetrosis should also be distinguished from the much milder autosomal dominant adult disease and the carbonic anhydrase II deficiency syndrome which is associated with renal tubular acidosis and less severe osteopetrosis.5 ,6