The Hospital Readmissions Reduction Program targets Medicare patients with congestive heart failure (CHF) and chronic obstructive pulmonary disease (COPD) and penalizes hospitals that have increased 30-day readmission rates for these patients. The main goals of this study were to determine the clinical explanations for readmissions within 30 days, to identify possible deficiencies in patient care, and to identify typical characteristics of patients who were readmitted to the hospital.