Control of arterial blood pressure at near-normal levels is of importance for the prognosis of patients with Type 1 (insulin-dependent) diabetes mellitus. In non-diabetic populations patient compliance to antihypertensive therapy is frequently poor, especially in young people. Thirty-seven consecutive eligible patients with longstanding Type 1 diabetes and persistently uncontrolled hypertension were questioned about their preferences regarding hypertension treatment. Throughout they expressed a strong desire for more information about hypertension and for active participation in monitoring of blood pressure and therapeutic decision-making. In addition, they showed considerable reluctance to accept a pharmacological intervention. Therefore, in order to improve blood pressure control, the patients participated in a structured outpatient hypertension treatment and teaching programme for groups of about 6 patients consisting of four teaching sessions at weekly intervals. The programme comprised home-monitoring of blood pressure and involvement of the patients in treatment decision-making. In 34 patients who had a complete follow-up examination after an average of 16 months, mean sitting arterial pressure had decreased from 111 to 101 mmHg (p less than 0.001) and 53% of the patients were below 140/90 mmHg. The number and dosage of prescribed antihypertensive agents remained unchanged by the intervention. Sodium intake was not reduced during the study, but pulse rate decreased significantly in patients treated with beta-adrenergic blockers and serum uric acid rose in patients on diuretic therapy, suggesting increased adherence of the patients to prescribed antihypertensive drug therapy. In 34 comparable Type 1 diabetic patients who were not subjected to a hypertension treatment and teaching programme mean arterial blood pressure remained unchanged during a 12-month period.