Severe osteogenesis imperfecta results in frequent fracturing of lower extremity bones when the child assumes upright weightbearing. To prevent such breakage and to provide simple, comfortable standing, a special "vacuum pant" orthosis was designed and assessed in four patients. Not only has this enabled the family to help their children stand up safely and comfortably, but the frequency of fracturing has diminished. Bone densitometry studies of the tibia revealed an increase in both the mineral content (0.39 to 0.70 g/cm) and the bone density (0.44 g/cm2) above that expected for growth alone in one patient. The "vacuum pant" orthosis is a useful addition to the treatment program of the severe osteogenesis imperfecta child.