Profile of MIB-1/Ki67 in 10 pheochromocytoma cases Pheochromocytoma, is a paraganglioma of the adrenal medulla. Though 10 % of the cases may show malignant biological behavior, there are no reliable morphological parameters. MIB-1/Ki-67 labeling indices of ten pheochromocytomas have been compared with histopathological features, ie., vascular invasion, local extension, necrosis, diameter of the tumour and S-100 protein positive sustentacular cells. The mean of MIB-1 labeling index is 1.78±1.65, with a range of 0.1%-5.5%. With a cutoff point of 2%, tumours having MIB-1 labeling index greater then 2 % showed necrosis and/or vascular-capsular invasion. Also tumours with MIB-1 labeling index >2 % contained decreased amounts of S-100 protein-positive sustentacular cells which has been previously shown to be correlated with prognosis. The prognostic importance of MIB-1 labeling index as a proliferation marker in pheochromocytoma has to be evaluated in larger serises with metastasis-free survival.