The investigators have currently finished conducting an international multi-center trial that compares the efficacy and safety of pamidronate and zoledronate in the treatment of moderate to severe forms of Osteogenesis Imperfecta (OI). This trial has included only children above one year of age. The aim of the current study is to extend the observations of that currently finished study to infants below 1 year of age. Moreover, it is possible to administer zoledronate in a single short infusion instead of the three-day cycles with Pamidronate, therefore decreasing patient and family burdens with shorter stays in the hospital.

Inclusion Criteria:

• Children, male or female 2 weeks to < 12 months of age, at least at 38 weeks gestational age.
• Any child with phenotypic OI type II, III or IV.
• Any child classified as OI type I, V-VIII that has had at least two or more previous fractures of long bone, or vertebral compression fractures, and a low bone mineral density.
• No previous treatment with bisphosphonates.
• Negative urine protein as measured by dipstick. One repeat assessment of the urine protein will be allowed.

Exclusion Criteria:

• Blood oxygen saturation of less than 90% in room air.
• Serum creatinine level greater than 56 µmol/L.
• Any clinically significant clinical laboratory abnormalities at screening.
• Treatment with any investigational drug within the past 30 days.
• Patients who are unlikely to be able to complete the study or comply with the visit schedule.
• Any disease or planned therapy which will interfere with the procedures or data collection of this trial.