Background: Hypertension is the most prevalent controllable lethal disease in the present century and is one of the most common causes of visits in private offices and general clinics. In our region, no extensive study has been done on the incidence and PRECIPITATING FACTORS of hypertensive crisis in patients with primary hypertension. Given the very large number of patients referring for this reason to Mashhad and especially in Imam Reza (A.S.) Hospitals, this study was conducted with the aim of determining the incidence of hypertensive crisis and its PRECIPITATING causes and proposing plans to control these FACTORS.Methods: A prospective study was done on hypertensive patients referring for hypertensive crisis in the cardiac emergency room of Imam Reza (A.S.) Hospital during an 18-month period from August 2002 to March 2004. By definition, a diastolic blood pressure of 140 mmHg or higher was set for choosing patients, and on this basis 192 patients entered the study. Study subjects were selected from patients aged 30 to 75 years, and an effort was made to ensure that all the subjects had primary hypertension.Results: Among the 192 patients, males comprised the higher percentage. Hypertensive crisis. occurred most commonly in patients aged 50 to 60 years, followed by those above 70.75% of the patients had stopped taking medications for a long time, and the most common reasons for this were a feeling of improvement, growing tired of the long-run medications, being on a journey with the drugs left at home, and side effects, respectively. This study proved emotional stress and diet changes, especially taking excess salt, as important PRECIPITATING FACTORS.Conclusion: Hypertension is an important threat to general health in the developed countries, and has the characteristics of being common, asymptomatic, and easily detectable and treatable. A potentially fatal complication of hypertension is hypertensive crisis. This study was conducted with the aim of determining the incidence and the causes of hypertensive crisis and proposing ways to prevent its occurrence. It is recommended that the drugs should be taken life-long and not stopped without doctor's permission. The patients should be careful to take along their medications on trips and to continue to observe a low-salt diet.