Compliance to antihypertensive treatment is a critical factor conditioning the success of therapy. It has been calculated that, depending on the method used to monitor compliance, only 20 to 80% of treated hypertensives can be considered as good compliers. In the past years it was thought that compliance was only a patient's problem but instead, the role of the physician in determining patient's compliance is very important. He should give clear information about the risks of the disease, the advantages of therapy and how to take medicines. He should also prescribe a therapeutic scheme as simple as possible avoiding multiple drug administrations and informing patients about possible side-effects. Subjects at particular risk of poor compliance (middle aged males, still active in work, without previous cardiovascular diseases) must be particularly monitored. In any case of poor response to therapy it is important to suspect poor compliance. A standardization of the methods for recording compliance is needed especially in clinical trials. The results of experimental studies in fact can be misleading if compliance is not taken into account.