Osteogenesis imperfecta is often regarded as a form of osteoporosis. In many cases, particularly those in whom the first fracture occurs outside the neonatal period, bones that have not been fractured may appear radiologically normal. In a group of 24 adults with osteogenesis imperfecta the thickness of the metacarpal cortex was normal but their bones were often slender. Osteoporosis is probably not an inevitable feature of such cases, and some of the radiological abnormalities reported may be the results of previous fractures and their treatment.