Osteoporosis is currently receiving increasing attention as an important late effect in survivors of childhood cancer and its treatment because of their quality of life and its negative effect on the survivors' ability to perform developmentally appropriate activities. Survivors of childhood cancer are especially vulnerable because they are affected during childhood and adolescence, a time when peak bone mass should be achieved. This paper reviews decreased bone density in acute lymphoblastic leukemia (ALL), which is the most common childhood cancer and has a cure rate approaching 80%. Osteopenia/osteoporosis has been observed in all phases of the disease: at diagnosis, during treatment, and throughout the post-treatment period for as long as 20 years. Among the findings that have been described are musculoskeletal pain, disturbed gait, fractures, kyphosis, lordosis, and growth failure. Risk factors not specifically related to ALL include smoking, ingestion of carbonated beverages, and family history of "brittle bone" or fractures. Patients should be counseled in regard to diet, exercise, smoking cessation, and avoidance of carbonated beverages. There are a number of options for specific drug therapy; however, the administration of bisphosponates to children and adolescents must be approached with caution. Research is needed to determine how extensive the problem is and how to best prevent and treat the osteopenia/osteoporosis associated with ALL.