Objective: To explore the determinants of postoperative outcomes of adrenal surgery in order to build a proposition for healthcare improvement. Summary of Background Data: Adrenalectomy is the recommended treatment for many benign and malignant adrenal diseases. Postoperative outcomes vary widely in the literature and their determinants remain ill-defined. Methods: We based this retrospective cohort study on the “Programme de médicalisation des systèmes d’information” (PMSI), a national database that compiles discharge abstracts for every admission to French acute health care facilities. Diagnoses identified during the admission were coded according to the French adaptation of the 10th edition of the International Classification of Diseases (ICD-10). PMSI abstracts for all patients discharged between January 2012 and December 2017 were extracted. We built an Adrenalectomy-risk score (ARS) from logistic regression and calculated operative volume and ARS thresholds defining high-volume centers and high-risk patients with the CHAID method. Results: During the 6-year period of the study, 9820 patients (age: 55 ± 14; F/M = 1.1) were operated upon for adrenal disease. The global 90-day mortality rate was 1.5% (n = 147). In multivariate analysis, postoperative mortality was independently associated with age ≥75 years [odds ratio (OR): 5.3; P < 0.001], malignancy (OR: 2.5; P < 0.001), Charlson score ≥2 (OR: 3.6; P < 0.001), open procedure (OR: 3.2; P < 0.001), reoperation (OR: 4.5; P < 0.001), and low hospital caseload (OR: 1.8; P = 0.010). We determined that a caseload of 32 patients/year was the best threshold to define high-volume centers and 20 ARS points the best threshold to define high-risk patients. Conclusion: High-risk patients should be referred to high-volume centers for adrenal surgery.