The only pheochromocytoma analyzed (n = 1) showed a distinct CD56++ CD57+ GD2++ CD271+ CD9+ CD81+ CD90het CD58+ phenotype, in the absence of expression of CD10, CD99, CD117, EpCAM, nuMyoD1, and numyogenin. The gene discussed is CD99; the disease is hereditary pheochromocytoma-paraganglioma.