The expected increase in the proportion of older persons over the next century underscores the need to identify modifiable risk factors for disease and disability in this population. One such risk factor is weight, which plays a role in many of the diseases common in old age and contributes to risk of disability and death. However, there is confusion and controversy regarding health risks associated with weight in old age. The emergence of new technologies to assess body composition should allow opportunities to better understand health risks associated with weight in old age, as suggested by the new report in this issue of the Journal. While application of these technologies to population studies will still require careful attention to methodological caveats important in studies of weight, the ability to separately examine lean mass, bone, and fat should shed light on the underlying biologic processes pertinent to risk.