Diuretics are commonly prescribed in older people and are often used for prolonged periods. Indications for their use include heart failure and hypertension. They are also used to empirically treat complaints such as swollen ankles and shortness of breath. The aging body is particularly susceptible to the adverse effects of diuretic therapy. Many of the problems are a result of intravascular and extravascular fluid imbalance. It is therefore important that diuretics are prescribed rationally and with good reason. Most major clinical trials do not include older people with multiple co-morbidities. This review will consider whether trials involving diuretics are any different, through an evaluation of what evidence there is to support diuretic use in older people. We will also evaluate the evidence which implicates diuretics as a cause of common clinical problems such as falls, postural hypotension and incontinence. Finally, a rational approach to the use of diuretics in older people will be suggested so that the benefits of diuretic therapy can be maximized and potential adverse effects minimized.