Readmissions represent a substantial burden to the health care system. Risk factors for 30-day readmission after adrenalectomy were examined. Patients who underwent adrenalectomy were selected from the American College of Surgeons National Surgical Quality Improvement Program database from 2011 to 2015. Among 4,221 patients who underwent adrenalectomy, 216 (5.1%) were readmitted. On multivariate analysis, pre-operative predictive factors associated with readmission were American Society of Anesthesiologists classification (odds ratio [OR] 1.4, confidence interval [CI] 1.1-1.8), disseminated cancer (OR 1.6, CI 1.1-2.5), and adrenal injury (OR 10.9, CI 1.8-68.9). Elective procedures had fewer readmissions (OR 0.50, CI 0.33-0.76). and procedures with greater relative value units had greater readmission rates (OR 1.01, CI 1.004-1.02). An open adrenalectomy (21% of patients) had a higher rate of readmission than a laparoscopic approach (8.0% vs 4.3%, OR 1.5, CI 1.1-2.0). Postoperative risk factors affecting readmission included reoperations (OR 3.2, CI 1.3-8.0), wound complications (OR 6.6, CI 3.8-11.7), systemic infection (OR 6.5, CI 3.9-10.7), renal complications (OR 7.1, CI 2.6-19.2), venous thrombotic events (OR 11.3, CI 5.6-22.6), and discharge to home (OR 0.40, CI 0.22-0.73). Encouraging the appropriate use of laparoscopic adrenalectomy, preventing venous thrombotic events and surgical infections, and improving early post-operative follow-up in high-risk patients may decrease readmissions.