1. This study includes 1038 patients (325 men and 713 women) who consulted the medical out-patient clinic, Rigshospitalet, Copenhagen, during the years 1932-38. All these patients had a blood pressure of 160/100 mmHg or 180 mmHg or more. 2. The average age at the first examination was 54 years; 97% were followed at intervals of 10 years until 1975, when sixty patients were still alive. Treatment was minimal until 1970. 3. Sixty percent of the men and 76% of the women reached an age of 65 years or more. Nine percent of the total patients lived to 85 years or more. Excess mortality was far higher in men than in women. 4. Causes of death were stroke in 17%, heart failure in 24%, coronary occlusion in 16%, uraemia in 4% and other diseases in 39%. At the first examination, thirteen cases of malignant hypertension were registered, none at later sessions.