Geriatric patients are a subset of older people with multiple comorbidities that usually have significant functional implications. Geriatric patients have impaired homeostasis and wide inter-individual variability. Comprehensive geriatric assessment captures the complexity of the problems that characterize frail older patients and can be used to guide management, including prescribing. Prescribing for geriatric patients requires an understanding of the efficacy of the medication in frail older people, assessment of the risk of adverse drug events, discussion of the harm:benefit ratio with the patient, a decision about the dose regime and careful monitoring of the patient's response. This requires evaluation of evidence from clinical trials, application of the evidence to frail older people through an understanding of changes in pharmacokinetics and pharmacodynamics, and attention to medication management issues. Given that most disease occurs in older people, and that older people are the major recipients of drug therapy in the Western world, increased research and a better evidence base is essential to guide clinicians who manage geriatric patients.