The modern treatment for childhood malignancy includes surgery and chemoradiotherapy either individually or in combination. Despite the great achievement in improving patient survival, these treatments also greatly enhance the adverse effects on the unfortunate children. Our research group has recently conducted a pioneer study on the bone mineralization and bone mineral density (BMD) study in longterm childhood cancer survivors in local patients who have completed anti-cancer treatment for at least five years. This landmark study showed that persistent treatment-related adverse effects on skeletal development are common (up to 50%) in local long-term survivors of childhood cancers. Thus, it is important during this critical period of rapid somatic growth in adolescents and young adults that these cancer survivors achieve their peak potential for bone mineralization and strengthening. In this proposed study, we investigate with a randomized and controlled study design on the efficacy of a second-generation oral bisphosphonate, alendronate, to improve BMD over a 36-week period in long-term survivors of childhood cancers in Hong Kong. In addition to alendronate, all subjects in the active and control groups will receive alfacalcidol (vitamin D) and calcium carbonate throughout the whole study period. The study results will help paediatric oncologists to decide on the optimal remedial treatments against osteoporosis in long-term cancer survivors.