Recognizing its limitations, we have accepted the name, congenital hyperphosphatasia, for a condition characterized by fragile bones, premature loss of teeth, and dwarfism. In the two children studied, the condition seems to be confined to bones and teeth, with other defects occurring secondarily. In bone, there were enormously increased synthesis and degradation in the subperiosteal areas, with associated lack of cortex formation and resultant weakness. In the teeth, there was osteoclastic resorption of dentin and replacement of the pulp by osteoid. This condition is quite different from the classic thin bone type of osteogenesis imperfecta, and consideration should be given to this difference in the planning of treatment.