A reclassification of osteogenesis imperfecta into a congenita type and two tarda types was made on the basis of ninety observed cases. The congenita type, in which the major lesions include blue sclerae and dentinogenesis imperfecta as well as osteoporosis, many fractures, and bowing of the bones, was seen in twelve patients. The two tarda types, differentiated on the basis of the presence or absence of bowing, were seen in forty-three and thirty-five patients, respectively. The frequency of other findings in the three groups is described, as well as differences in management, genetic pattern of inheritance, and course of the disease.