The ageing population presents various challenges for healthcare providers when prescribing medicines; two key factors of note are changes to the function of the kidneys and liver. It is common for physiological changes to occur in the kidney and liver during ageing, including a decrease in their volume, blood flow, and functional capacity. A reduction in kidney or liver function can have important implications on medication excretion and metabolism. This needs to be considered when prescribing and reviewing medications. The extent of alterations to function can be highly variable within a cohort of older people, and it is important to individually assess the degree of any kidney and liver impairment. Notably, there are also additional considerations associated with assessing kidney and liver function in older people. When kidney or liver function is reduced, it is important to consider changes to the pharmacokinetic properties of medications and adjust the drug dosage regimen accordingly, in order to reduce the risk of the older person developing side effects or toxicity from the medications. Additionally, it may be necessary to limit exposure to medications which could further cause kidney or liver injury. There may also be altered progression and prognosis of kidney and liver diseases, along with additional considerations in the management of these conditions, in older people.