Alendronate (Fosamax) is a drug that works by stopping bone resorption (break down). It has been used to treat post-menopausal osteoporosis, male osteoporosis and adults with osteoporosis due to long-term steroid therapy. The goal of this study is to determine the effectiveness of alendronate in children with idiopathic juvenile osteoporosis. Researchers believe that children treated with alendronate will improve bone strength and decrease the amount of fractures caused by osteoporosis.