Background: Recent studies have shown that a minimum of approximately one-third of one normal adrenal gland is required for sufficient adrenocortical stress capacity. Correlation between intraoperative measurement, determination of remnant size by computed tomography (CT), and adrenocortical stress capacity has not been examined so far. Methods: Twenty-two patients with familial pheochromocytoma (n = 13), sporadic pheochromocytoma (n = 3), and adrenocortical tumors (n = 6) who underwent unilateral or bilateral subtotal adrenalectomy (STAE, 28 adrenal remnants) were prospectively studied. Patients were examined in a multi-slice CT to determine residual adrenal tissue and by ACTH test 4 days and 3 months postoperatively. Results: There was a slight significant correlation between intraoperative and CT calculated volumes (r = 0.77, p < 0.001). However, volumes assessed by CT were almost doubled compared with intraoperative determination (p < 0.001). Although recovery of adrenal function could be observed, no significant changes of remnant volumes could be detected within 3 months. In patients with familial pheochromocytoma, there was a significant correlation between residual adrenal volume and stimulated cortisol levels (P < 0.001). A distinct minimum of adrenal volume for intact adrenocortical stress capacity could not be exactly determined, however, in one patient with only 10% residual adrenal tissue intact stress capacity was found. Conclusions: Residual adrenal tissue of approximately 10-15% offers intact stress capacity. However, an exact determination of the size of an adrenal remnant after STAE has limitations. CT gives larger volumes compared with intraoperative determination. For calculation of a volume-function correlation of residual adrenal tissue, in clinical practice, the determination of relative adrenal residual volume is acceptable. © 2008 Société Internationale de Chirurgie.