Scintigraphy with 131I-MIBG has located most pheochromocytomas. The detected tumors have been intra-adrenal, extra-adrenal, malignant, and familial in type. The method is safe, but requires images taken over three days to attain optimal results. Because of its ability to screen all sites where primary pheochromocytomas may reside, scintigraphy should be employed as the initial procedure in the search for these tumors. It may be the only technique that will locate extra-adrenal pheochromocytomas. The rate of false-negative results is about 10 percent; therefore, other techniques such as computed tomography will be necessary to help find the few elusive pheochromocytomas.