This study aims to examine the frequency of the pheochromocytoma (pheo), defined as a "benign, intra-adrenal, hypertensive, sporadic, unilateral tumor." Three large series amounting to 310 subphrenic chromaffin tumors operated over periods of 17, 23, and 41 years, respectively, have been reviewed. Among those combined 310 pheos, 48 (15.5%) were malignant (i.e., metastatic) and 262 (84.5%) were benign; 42 (13.5%) were ectopic (35% of malignant tumors versus 9.5% of benign tumors); 230 (74.2%) were hypertensive (74% of benign tumors versus 73% of malignant tumors); 29 (9.4%) were bilateral, including 23 patients with a family history; 41 (13.2%) of patients had MEN II type A or B syndrome; and 20 (6.5%) occurred in a phacomatosis setting. Some of the patients had a non-MEN family history of pheo (n = 5), seemingly sporadic hyperparathyroidism (n = 4), or other associated neuroendocrine tumor (n = 9). Sometimes several of these features were combined. Finally 125 (40.3%) cases fitted the classic description of the tumor, 47.0% at the time of initial presentation and 40.3% at the end of follow-up. Late occurrence of metastases or metachronous diagnosis of familial disease make lifelong follow-up mandatory. Genetic studies may be indicated in pheochromocytoma patients.