One hundred twenty-seven children with osteogenesis imperfecta (O.I.) were studied during the first 10 years of life. According to Sillence, 40 patients were assigned to type I, 39 to type III, and 48 to type IV O.I. Centiles for height, weight, and the annual number of fractures could be established for the different types of O.I. The development of the skeletal changes could be documented for the different forms of the disease. At birth, the skeletal changes were significantly more severe in type III than in type IV patients. During the first 10 years of life the number of fractures, extent of skeletal deformities, and growth retardation did not differ between types III and IV. Only fracture nonunion, dentinogenesis imperfecta, and congenital cardiac malformations were more frequent in type III than in type IV. Papillary calcifications of the kidney and kidney stones were diagnosed in 4 type III and 2 type IV patients. Hemihypertrophy of the body developed in 2 type I patients. Although types III and IV patients suffered from severe short stature, serum insulin-like growth factor (IGF) I was in the normal range.