Postoperative neck hematoma is a well-known complication of thyroid and parathyroid surgery. Better understanding of risk factors for hematoma formation will help define high-risk populations. To examine possible risk factors for neck hematoma after thyroid or parathyroid surgery. Retrospective analysis of hospital discharge data from the Nationwide Inpatient Sample database. Using the International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis and procedures codes, we identified adults who underwent thyroid or parathyroid surgery and in whom neck hematoma subsequently developed. Information about demographic, clinical, and hospital characteristics was collected. Multivariate regression analyses were used to predict independent risk factors for neck hematoma. We identified 147,344 thyroid and parathyroid operations performed nationwide between 2000 and 2009. Overall incidence of postoperative neck hematoma was 1.5% (n = 2210). In multivariate analysis, age 65 years and older (odds ratio [OR] = 1.8, 95% confidence interval [CI] = 1.4-2.1), male sex (OR = 1.3, 95% CI = 1.2-1.4), African-American race (OR = 1.5, 95% CI = 1.2-1.7), being from the South (OR = 1.3, 95% CI = 1-1.4), comorbidity score of 3 or more (OR = 2, 95% CI = 1.6-2.6), history of alcohol abuse (OR = 2.7, 95% CI = 1.6-2.5), Graves disease (OR = 3, 95% CI = 2.1-4.1), and substernal thyroidectomy (OR = 3.3, 95% CI = 2.8-3.9) were associated with a higher risk of neck hematoma. We identified demographic and clinical factors associated with increased risk of neck hematoma after thyroid or parathyroid surgery.