Pheochromocytoma is surgically curable, and lethal complications often ensue when the diagnosis is not made. We review 54 autopsy-proven cases of pheochromocytoma seen at the Mayo Clinic over the 50-year period 1928-1977. There were 31 females and 23 males, and the patients' ages ranged from 40 hours to 92 years (mean, 53 years). Pheochromocytoma was multiple in 10 patients (19%), extra-adrenal in 5 (9%), and malignant in 6 (11%). In 13 (24%) pheochromocytoma had been correctly diagnosed in life--after the investigation of hypertension in 8 patients, incidentally at laparotomy for unrelated conditions in 4 patients, and in association with the multiple endocrine neoplasia syndrome in 1 patient. In the group of 41 patients (76%) in whom pheochromocytoma had not been suspected clinically, hypertension also was a common finding (22 patients, 54%). Symptoms such as headache, sweating, and palpitations were nonspecific, but all occurred more often among the group of patients in whom the diagnosis had been made. For both groups, hypertensive or hypotensive or hypotensive crisis precipitated by surgery for unrelated conditions was a common cause of death. Prevention of such deaths requires a high degree of clinical alertness and biochemical screening tests for pheochromocytoma in patients with labile or accelerated hypertension.