The aging process is characterized by a high level of complexity, which makes the care of older adults particularly challenging. This complexity results from the presence of an array of concomitant clinical conditions, whose integration and cumulative effect result in different degrees of functional deficits, cognitive deterioration, nutritional problems, geriatric syndromes in addition to lack of social support and financial resources. The presence of these factors may reduce the efficacy of prescribed drugs and increase the risk of iatrogenic illness making the pharmacologic treatment of this complex patient a difficult task for the prescribing physician. The presence of renal disease further contributes to increasing this complexity and to increasing the risk of iatrogenic illness because it is associated with pharmacokinetics and pharmacodynamics that may alter drug metabolism. For this reason, a complete and global examination of patient characteristics is mandatory in the drug prescribing process. Assessment of renal function must be considered part of this process.