The risk for bilateral tumors and long-term outcome after conservative cortical-sparing adrenal surgery was studied in a consecutive single-center series. One hundred fifty-four patients were operated on (1950-2004) for pheochromocytoma (PC=137), or abdominal paraganglioma (PG=17). Twenty had MEN 2 (16 MEN 2A; 4 MEN 2B), 15 von Recklinghausen's disease (VRD), and 1 von Hippel-Lindau (VHL) disease. Twelve patients had, or developed, bilateral adrenal medullary tumors; four with MEN 2A, four with MEN 2B, three with VRD, and one with probably hereditary PC associated with brain tumors/meningioma. Two patients with MEN 2B and one with MEN 2A with had bilateral adrenalectomy (adx). Three VRD patients, two MEN 2B and one MEN 2A patients had cortical-sparing surgery. Two patients were operated on unilaterally, but developed small contralateral tumors; one of these (MEN 2A) had a second asymptomatic PC diagnosed at an older age, so surgery was withheld; the other patient (hereditary PC syndrome) had a small contralateral PC diagnosed at autopsy 9 years later. Only three of nine patients with bilateral operations needed corticosteroid replacement after surgery. Four of six patients died of associated tumors (MTC and meningioma). The mean follow-up was 13 (1-25) years. Twelve MEN 2A patients with unilateral adx have been followed up for 20 (4-36) years without developing a second PC. Cortical-sparing adrenal surgery can safely be performed in the majority of patients with bilateral PC. On the basis of our long-term experience of MEN 2A we perform contralateral adrenal resection only if a second PC is confirmed. Five patients underwent adrenal exploration because of clinical and biochemical findings compatible with PC. Four had asymmetrical positive MIBG scans. They all underwent unilateral adx and diffuse medullary hyperplasia was confirmed (medullary weight estimated morphometrically to 1.0-3.4 g vs. normal weight 0.3-0.5 g in matched controls). These patients have been followed for 19 (5-27) years with normal clinical and biochemical findings. In this rare condition removal of the largest adrenal seems adequate.