The need to evaluate potential living kidney donors is more pressing than ever before. Evaluating the potential medical risks to individual donors presents both medical and ethical questions related to quantitative hazards of donor nephrectomy. These include conditions commonly associated with age, such as the decline in glomerular filtration rate, the rise in arterial pressures, and weight gain. The "normal" ranges for many of these characteristics are changing as their importance as predictors of cardiovascular risk is reevaluated and the duration of exposure for a lifetime is considered. Many older donors in good health favor donating a kidney to a spouse, despite the presence of elevated blood pressure or even impaired glucose tolerance. The Mayo Kidney/Pancreas transplant program established an "extended criteria workgroup" to address these issues on an individual basis. Our program now stratifies medical criteria based upon age, allowing more liberal criteria for older donors. As a result, we accept treated hypertension in white donors, emphasizing the importance of informed consent and the need for vigilant follow-up. Our greatest concern relates to the development of obesity, particularly in younger individuals. Many of the long-term results of kidney donation are likely to hinge upon future behavior, including smoking, weight management, and medical follow-up care. Older donors are more likely to have established behavior patterns, an element that makes them better candidates in many respects. Studies to closely track the impact of donor nephrectomy in the current era with changing population demographics and expectations are essential.