Truly adequate dialysis would restore patients to full health, with functional status and length of life indistinguishable from others of the same age, sex, and race without chronic kidney disease. We are far from achieving such outcomes, however, in part because of the dearth of available evidence on which areas of care should be emphasized to get the greatest clinical and psychosocial benefits at the most affordable costs. A clear understanding of the strengths and limitations of currently available evidence can help guide researchers and clinicians in this field, and likely will lead to increasing emphasis on identification and management of comorbid conditions and a focus on preventative medicine. Optimal dialysis will be accomplished only when normal kidney functions are mimicked by artificial devices to a much greater extent than is currently the case.