Growth deficiency is a key feature of severe Osteogenesis Imperfecta (OI) and a frequent feature of mild to moderate forms of the disease. The reason that children with OI are short is not fully understood. We do know that details such as the number of fractures suffered or the type of OI do not fully explain the short stature of OI. Growth patterns have been defined for children with OI Types I, III, and IV. At about 12 months of age, children with Types III and IV OI demonstrate a predictable plateau of their linear growth rate. Type IV OI children begin to resume a normal growth rate at about age four to five years, but they will not "catch up" to a normal height, as they have "lost" a significant period of growth. The plateau usually continues for children with Type III OI. The reason for this growth plateau is unknown. There have been no studies which evaluate the growth of OI children in this age range. Our previous studies of growth in OI children have begun at age 5 years. We have studied growth in OI children for the past 10 years. Different medications have been tried to both stimulate growth and improve bone density. Some children have responded to growth hormone (their growth rate increased by at least 50%) and some did not. The majority of children who did respond were Type IV. However, we need to carefully treat and study more children to try to determine which children will benefit from growth hormone medication. The Goals of this Study Are: 1. We want to try to find a cause for the growth plateau common in types III and IV OI. Long-term, our goal is to develop a treatment to eliminate this plateau. 2. We want to see how long and how well OI bone will respond to growth stimulation. 3. We hope to find a "predictor" for who will respond to growth hormone and who will not, by measuring your child's endocrine and growth hormone function before receiving any growth hormone treatment. 4. We want to measure the effects of growth stimulation on bone density, and the quality of OI bone. 5. We want to see if there are long term benefits resulting from this treatment in the form of final adult height, trunk height, and possibly improved function of the respiratory system. Median Subject Age (on p. 1 of webpage): 1-15 years (replaces 0-20)