The disease of which an illustrative case is reported below was first described in 1833 by Lobstein27, who gave it the name of ' osteopsathyrosis (o&rEov =a bone, laOvp4v =friable). According to his original description it is characterized by the appearance in certain families of cases of undue fragility of the bones. This fragility manifests itself in a tendency of the bones to break as the result of slight violence. On the other hand, repair of the fractures takes place not less rapidly than in normal bones.Since the publication of Lobstein's work many other cases of the disease have been recorded, and a clinical picture has gradually emerged in which fragility of the bones appears as one of a group of associated abnormalities. Many of these are exemplified in the case now to be described.Case report.The patient, a maryied woman of 35, came to the New Sussex Hospital complaining of curvature of the spine, present since the age of 10 years, and of paini in the back for the last few months. She stated that since the birth of her only child, 5 years ago, she has noticed that her eyes were getting blue. This blueness is said by her sister, however, to have been present for at least 8 or 10 years. Four years ago she began to be deaf in the right ear, as the result, she thought, of a cold. She was treated by politzerization but the deafness was not relieved. It grew gradually worse, and the left ear began to be affected. Ringing noises were noticed, first in the right ear and later in the left ear also. She broke her left humerus at the age of 12 years, from a fall while jumping at school, and shortly afterwards broke the left ulna twice in succession from falls in the school playground. PHYSICAL EXAMINATION.-Patient is a small woman (about 5 ft. in height), healthy looking and (for her size) of fair muscular development. She is so deaf that the voice must be raised in speaking to her. The sclerae are of a moderately deep indigo blue colour, and each cornea shows a well-marked arcus senilis. The upper teeth are false. The lower incisors are small and thin, and the enamel worn away towards the free edge, which has a mouse-eaten appearance. The remaining teeth appear normal. There is a severe structural scoliosis (single curve, convex to the left, apex at the loth-ilth dorsal vertebra). The