IT HAS BEEN a decade since the 1984 Consensus Development Conference on Osteoporosis first suggested that increased intake of calcium might help prevent osteoporosis. Osteoporosis affects more than 25 million people in the United States and is the major underlying cause of bone fractures in postmenopausal women and the elderly. Previous surveys have revealed that the US population experiences more than 1.5 million fractures annually at a cost in excess of $10 billion per year to the health care system. Two important factors that influence the occurrence of osteoporosis are optimal peak bone mass attained in the first two to three decades of life and the rate at which bone is lost in later years. Adequate calcium intake is critical to achieving optimal peak bone mass and modifies the rate of bone loss associated with aging.