The U.S. population is aging, bringing with it an increased prevalence of chronic disease and concomitant declines in physical function. The risk of developing cancer increases significantly with age, and functional decline is much more likely once a cancer diagnosis is rendered. Thus, functional status in later life is a key concern, one that is heightened among elders who have been diagnosed with cancer. To date, however, there have been few trials that have exclusively addressed issues related to cancer survivorship among older cancer patients, and to our knowledge, none has focused on preserving or enhancing physical functioning. This paper describes the study design and methodological considerations of a randomized controlled trial to determine if a personally tailored workbook and telephone counseling program can positively affect physical activity and dietary behaviors and ultimately the physical functioning of up to 420 older men and women newly diagnosed with breast or prostate cancer. This trial is unique because the cancer diagnosis is used not only as a marker of risk for functional decline, but also as a "teachable moment" - an opportune time when elders may be more receptive to making beneficial lifestyle changes. Undoubtedly, as cure rates for cancer increase and intersect with ever-growing numbers of elderly, there will be numerous opportunities to provide and test interventions within this vulnerable population and to target functional status as a primary outcome. In reporting our methods, we hope to give others "a leg up," so that they can hurdle with greater ease the barriers we experienced, and thus advance the field more rapidly. © 2003 Elsevier Science Inc. All rights reserved.