Malignant infantile osteopetrosis is a rare inherited disease of bone metabolism, in which osteoclast dysfunction and diminished bone turnover lead to diffuse sclerosis with obliteration of the medullary cavities and narrowing of the skull base neural foramina. We report a case of malignant infantile osteopetrosis with bone marrow failure and optic atrophy that co-occurred with hypophosphatasia, another rare inherited bone disease, in a 6-year-old boy. Key imaging signs of these rare diseases are discussed.