In the years 1977 to 1981, 47 cases of phaeochromocytoma and 19 cases of aldosterone-producing adrenal adenoma (Conn's syndrome) were diagnosed in Denmark as reported to the National Register of Hospital Patients. This corresponds to an average annual incidence of phaeochromocytoma and Conn's syndrome of 1.9 and 0.8 per million inhabitants, respectively. Treatment results were evaluated from the patient's records and follow-up questionnaires. Of 30 surviving patients operated upon for phaeochromocytoma and followed-up after 18-81 months, 23 were normotensive without treatment and seven were mildly to moderately hypertensive. Of 11 patients operated upon for Conn's syndrome, follow-up data at 1-2 years were obtained in seven, of whom five were normotensive and two hypertensive. Phaeochromocytoma and Conn's syndrome are rare diseases. The results of surgical treatment are often gratifying, but not all patients remain normotensive after surgery, even in the absence of recurrence of endocrine disease.