Pheochromocytoma was suspected in the case of a 16-yr-old girl with a history of severe headache for about a year and systolic blood pressures exceeding 240 mm Hg. She was treated with phentolamine by mouth to lower her blood pressure and expand her blood volume, but after 5 days there was no further response to either oral or intravenous administration. During operation her blood pressure was successfully controlled by an intravenous infusion of sodium nitroprusside. A pheochromocytoma weighing 29 gm was removed. By the sixth postoperative day the systolic pressure had been reduced to 124 mm Hg, papilledema had subsided, and the patient was able to leave the hospital.