Increasing numbers of patients are receiving warfarin therapy, with atrial fibrillation being the main indication. If warfarin therapy is to be effective, however, good therapeutic control is important. Recent advances in models of management, including primary care clinics and patient self-management, has meant that patients have an increasing choice as to how and where they have their warfarin monitored. Comparison of performance between these different models of care has been historically difficult due to the use of different reporting techniques. This paper highlights the different methods of reporting therapeutic control, including adverse event reporting, and recommends that at least two measures from a set of recognised parameters should be used. This makes comparison of control between centres possible.