A unilateral, apparently sporadic pheochromocytoma was removed from the right adrenal of a 73-yr-old Caucasian woman. At the time of surgery, germline DNA from the patient was not available. However, a continuous cell line (KNA) established from the tumor showed a heterozygous sequence variant TGC (cysteine) to TGG (tryptophan) in exon 10, codon 611 of the RET proto-oncogene. Subsequent genetic testing of the patient and her offspring revealed the same base-change in herself, one daughter, one son, and the only grandson, confirming hereditary disease classified as MEN2A-2. Clinical follow up of the patient revealed elevated serum calcitonin after 6 yr. Thyroidectomy was performed and revealed a small medullary thyroid carcinoma. The patient's children thus far show no evidence of MEN2, but C-cell hyperplasia has been diagnosed in the grandson. Our serendipitous finding of a MEN2A-2 mutation in a patient with initial diagnosis of late onset, unilateral, "sporadic" pheochromocytoma would argue for routine mutation screening of even elderly patients presenting with a pheochromocytoma.