Pheochromocytoma is a catecholamine-secreting tumor derived from chromaffin cells of the adrenal medulla and extra-adrenal sympathetic and parasympathetic tissue. Diagnosis should be made by hormonal tests and supplemented with imaging techniques such as tomography (CT) and/or magnetic resonance imaging (MR). To confirm its location and the existence of multiple tumors, it is necessary to perform a functional test, the iodo-methyl-benzylguanidine (IMBG) scintigraphy being the test of choice. Its sensitivity decreases in extra-adrenal location pheochromocytomas or malignant tumors. Two cases are reported in which, despite high clinical suspicion of recurrence of pheochromocytoma, the IMBG scintigraphy was negative. The positron emission tomography (PET-CT) using 18-fluorodeoxyglucose (18F-FDG) was essential for the diagnosis in both cases. In addition, the need for a genetic study in some cases of non-syndromic pheochromocytoma is discussed.