We evaluated the long-term use of synthetic salmon calcitonin in the management of osteogenesis imperfecta tarda and congenita. Forty-eight children, ranging in age from 6 months to 15 years, and two young adults, received synthetic salmon calcitonin 2 MRC units/kg three days a week and a daily oral calcium supplement of 230 to 345 mg. The annual fracture rate was decreased during calcitonin therapy as compared to the period preceding therapy. There was an increase in the ability of the patient to stand and move and in the subjective feeling of strength in the lower extremities during calcitonin therapy. There was also a significant improvement in radiographic bone density, as determined by the method of photodensitometry, in patients under 5 years of age. Long-term administration of synthetic salmon calcitonin may be beneficial to young children with osteogenesis imperfecta.