Recently published American and British guidelines have comprehensively reviewed the indications for long term anticoagulation. The best evidence currently available supports the use of long term oral anticoagulants in patients with nonvalvular atrial fibrillation (NVAF), venous thromboembolic disease, ischaemic heart disease, mural thrombi, and mechanical heart valves. Selected patients with valvular heart disease, cerebral vascular disease, and peripheral arterial disease may also benefit from the use of these drugs. When no specific contraindications are present, elderly patients with either paroxysmal or persistent NVAF should be considered candidates for treatment with anticoagulants. Pooled analyses of the results from 9 randomised trials demonstrate that warfarin significantly reduces the risk of ischaemic stroke in patients with NVAF, particularly those in a 'high risk' category defined by the presence of additional clinical or echocardiographic risk factors. Long term anticoagulation does not appear to be justified in patients with NVAF considered to be at 'low risk' for stroke. Because the prevalence of NVAF and most other cardiovascular conditions increases with advancing age, many elderly patients will be candidates for thromboprophylaxis. The potential benefit of long term anticoagulation must be carefully weighed against the risk of serious haemorrhage in such patients. Bleeding complications with anticoagulant drugs appear to occur more frequently in older patients than in younger individuals. Advanced age (>75 years), intensity of anticoagulation [International Normalised Ratio (INR) >4.0], history of cerebral vascular disease (recent or remote), and concomitant use of drugs that interfere with haemostasis [aspirin (acetylsalicylic acid) or nonsteroidal anti-inflammatory drugs] are among the most important variables in determining an individual's risk for major bleeding with anticoagulants. Older patients often display increased sensitivity to the effects of warfarin, both in the early induction phase and during the long term maintenance phase of therapy. Conditions such as congestive heart failure, malignancy, malnutrition, diarrhoea and unsuspected vitamin K deficiency, enhance the prothrombin time response. The decision to interrupt anticoagulant therapy before elective surgery in elderly patients should evaluate the thrombotic risk of such a manoeuvre versus the risk of bleeding if anticoagulants are continued. In non-surgical patients, excessively elevated INRs without associated haemorrhage can usually be managed by simply witholding one or several doses of warfarin. If more rapid reversal is needed, small doses of phytomenadione (vitamin K1) can be administered safely without overcorrection or the development of vitamin K-induced warfarin resistance.