Alendronate (Fosamax (Trademark), Merck & Co.), an aminobisphosphonate, is a potent inhibitor of bone resorption. It has been used to treat postmenopausal osteoporosis, idiopathic male osteoporosis, and glucocorticoid induced osteoporosis in adults. The goal of this protocol is to evaluate the effectiveness of Alendronate in children with glucocorticoid induced and idiopathic juvenile osteoporosis using a double-blind, randomized, placebo-controlled study design. We hypothesize that children treated with this drug will have an improvement in bone mineral density and decrease in osteoporotic fractures.