A clinical study was performed on 940 cases of essential hypertension observed at Dept. of Internal Medicine of Seoul National University Hospital during a period of last seven years from 1971 to 1977. The followings were the results: 1. The incidence of hypertensive patients was 13.8% among all medical in-patients and 68.2% among all cardiac in-patients. 2. The highest occurence was observed in sixth decade and accounted for 34.2% of all cases and least occurence was in second decade of life which accounted for 0.6% of all cases. No difference was found in age distribution between both sexes. The male to female ratio was 1.2:1. 3. The mean value of blood pressure was 178.1+/-21.8/107.4+/-12.3 mmHg and tended to increase with age at least over the decades from second to seventh and there was tendency to decrease after the eighth decade. No paticular difference in blood pressure levels was found in both sexes. 4. The most outstanding symptom was headache which was found in 51.5% of all cases. Dizziness, dyspnea and palpitation were the next orders in frequency. There was a general trend of the the subjective symptoms which were more pronounced in younger than older patients. 5. Hypertensive retinopathy was found in 83.3% of all cases. Hypertensive retinopathy of K-W grade II was found in 36.1% of all cases and was the most frequent finding among the Keith-Wagener grades. Malignant hypertension of K-W grade IV was found in 4.2% of all cases and the largest numbers were between the fourth and fifth decade of life. 6. The abnormal retinal finding was found to be rather proportional to the blood pressure levels. 7. Albuminuria was detected in 56.2% of all cases and it was more frequent in male than in female patients. 8. The appearance of albuminuria seemed to have a close correlation with hypertensive retinal change and blood pressure levels. 9. Electrocardiographic abnormalities were associated in 71.9% of all cases. The most frequent association among electrocardiographic abnormalities was left ventricular hypertrophy which accounted for 45.2% of all cases. There was the reverse correlation between the normal electrocardiogram and degree of blood pressures. The finding of left ventricular hypertrophy and degree of blood pressures were closely correlated. 10. Cerebrovascular accident, renal failure, congestive heart failure and atrial fibrillation were four major complications. It was recorded in 26.5%, 10.4%, 5.4% and 2.0% of all cases respectively. The complications were common in men than in women. 11. Renal failure, congestive heart failure and myocardial infarction were closely corelated with hypertensive retinopathy.