Arterial hypertension is a serious public health problem worldwide. Indeed, its complications cause 9.4 million deaths annually. Hypertension is also a health problem with high impact in Chile. In fact, the National Health Survey 2009-2010, conducted by the Ministry of Health, showed a prevalence of 26.9%. Arterial hypertension is defined as systolic blood pressure (SBP) 140 mmHg and/or diastolic blood pressure (DBP) 90 mmHg. Traditionally, hypertension has been classified into primary or essential, which represents over 90% of adults with hypertension; and secondary, which includes less than 10% of hypertensive patients. The initial evaluation of a patient with hypertension should: 1) Confirm the diagnosis of hypertension; 2) Detect causes of secondary hypertension; and 3) Assess cardiovascular risk, organ damage (OD) and concomitant clinical conditions. This calls for blood pressure (BP) measurement, medical history including family history, physical examination, laboratory investigations and further diagnostic tests. A specific, potentially reversible cause of BP elevation can be identified in a relatively small proportion of adult patients with hypertension. However, because of the overall high prevalence of hypertension, secondary forms can affect millions of patients worldwide. A secondary form of hypertension can be indicated by a severe elevation in BP, sudden onset or worsening of hypertension, poor BP response to drug therapy and OD disproportionate to the duration of hypertension. If the initial assessment suggests that the patient has a secondary hypertension, then you should take into consideration the relevant causes, which are described in this article.