Pheochromocytoma has been reported to be inherited as a dominant trait with a high degree of penetrance.1 The patient presented in this paper is of special interest since it is the first reported case of pheochromocytoma in one identical twin. Homozygocity was established primarily by blood groupings performed at the Boston Children's Hospital Blood Grouping Laboratory where all factors tested were identical. In addition facial features (Fig 1) and finger prints assisted in twin verification. Of interest from a clinical standpoint was the difficulty encountered in diagnosing the pheochromocytoma in this patient due to the associated renal artery compression which contributed to the hypertension on a renal ischemic basis.
A 47-year-old man was admitted to the hospital on Oct 5, 1963, shortly after sudden onset of left hemiparesis. A history revealed that this man was first found to have hypertension at 16 years of age and had