The rapid growth of the oldest age groups will have a major impact on future health care costs. We use current US Census Bureau projections for the growth of our oldest age groups to project future costs for Medicare, nursing homes, dementia, and hip fractures. Without major changes in the health of our older population, these health care costs will escalate enormously, in large part as a result of the projected growth of the "oldest old," those aged 85 years and above. Medicare costs for the oldest old may increase sixfold by the year 2040 (in constant 1987 dollars). It is unlikely that these projected increases in health care costs will be restrained solely by cost-containment strategies. Successful containment of these health care costs will be related to our ability to prevent and/or cure those age-dependent diseases and disorders that will produce the greatest needs for long-term care.