Emergencies and hypertensive crises are clinical situations which may represent more than 25% of all medical emergency care. Considering such high prevalence, physicians should be prepared to correctly identify these crises and differentiate between urgent and emergent hypertension. Approximately 3% of all visits to emergency rooms are due to significant elevation of blood pressure. Across the spectrum of blood systemic arterial pressure, hypertensive emergency is the most critical clinical situation, thus requiring special attention and care. Such patients present with high blood pressure and signs of acute specific target organ damage (such as acute myocardial infarction, unstable angina, acute pulmonary edema, eclampsia, and stroke). Key elements of diagnosis and specific treatment for the different presentations of hypertensive emergency will be reviewed in this article. The MedLine and PubMed databases were searched for pertinent abstracts, using the key words "hypertensive crises" and "hypertensive emergencies". Additional references were obtained from review articles. Available English language clinical trials, retrospective studies and review articles were identified, reviewed and summarized in a simple and practical way. The hypertensive crisis is a clinical situation characterized by acute elevation of blood pressure followed by clinical signs and symptoms. These signs and symptoms may be mild (headache, dizziness, tinnitus) or severe (dyspnea, chest pain, coma or death). If the patient presents with mild symptoms, but without acute specific target organ damage, diagnosis is hypertensive urgency. However, if severe signs and symptoms and acute specific target organ damage are present, then the patient is experiencing a hypertensive emergency. Some patients arrive at the emergency rooms with high blood pressure, but without any other sign or symptom. In these cases, they usually are not taking their medications correctly. Therefore, this is not a hypertensive crisis, but rather non-controlled chronic hypertension. This type of distinction is important for those working in emergency rooms and intensive care unit. Correct diagnosis must be made to assure the most appropriate treatment.