Hyperthyroidism is associated with an elevated risk of cardiovascular events and worse hospital outcomes. The Nationwide Readmissions Database (NRD) 2018 was used to determine the characteristics of 30-day readmission in patients with hyperthyroidism. The 30-day all-cause readmission rate for hyperthyroidism was 10.3%. About 21.7% had hyperthyroidism as the principal diagnosis on readmission. Readmissions were associated with an increased odds of inpatient mortality (odds ratio, 7.04; 95% confidence interval [CI], 3.97 to 12.49), length of stay (5.2 days vs. 4.0 days; 95% CI, 0.7 to 1.8), total hospital charges, and cost of hospitalizations. Independent predictors of 30-day all-cause readmissions included Charlson Comorbidity Index ≥3 (adjusted hazard ratio [aHR], 1.76; 95% CI, 1.15 to 2.71), discharge against medical advice (aHR, 2.30; 95% CI, 1.50 to 3.53), protein-energy malnutrition (aHR, 1.54; 95% CI, 1.15 to 2.07), and atrial fibrillation (aHR, 1.41; 95% CI, 1.11 to 1.79). Aggressive but appropriate monitoring is warranted in patients with hyperthyroidism to prevent readmissions.