Refractory or resistant hypertension is an entity without a universally recognised definition. The ANAES (Agence Nationale d'Accréditation et d'Evaluation en Santé) working group in 1997 considered hypertension to be drug-resistant when, at two successive consultations (2 measurements at each consultation) the readings were > or = 160 mmHg for the systolic and or > or = 100 mmHg for the diastolic blood pressure despite triple therapy including a diuretic. These criteria were lowered to 140/90 mmHg in the latest ANAES recommendations published in 2000. The frequency of refractory hypertension varies according to the population studied and the recommendations. Resistance to therapy is usually multifactorial. If one of the main causes is volume overload due to inadequate diuretic therapy, risk factors to drug-resistance must be looked for and evaluated when antihypertensive therapy is started. If ambulatory blood pressure recordings or self-measured readings confirm that the hypertension is not controlled, it is recommended that the patient be referred to a specialised team to exclude unrecognised secondary hypertension or to adapt antihypertensive therapy.