Hospital readmissions are costly for patients and institutions. We conducted a study to evaluate rates of readmission within 30 days after anatomical total shoulder arthroplasty (ATSA) and reverse total shoulder arthroplasty (RTSA) and to determine independent risk factors for readmission. We queried the National Surgical Quality Improvement Program database for ATSAs and RTSAs performed between 2011 and 2013 and found a combined total of 3501 cases and an overall readmission rate of 2.7%. Of the readmissions, 67% were for medical complications, and 33% were for surgical complications. Of the medical complications, pneumonia was the most common (11.8%), followed by urinary tract infection (7.8%). Regarding surgical complications, surgical-site infection was the most common (13.7%), followed by prosthetic joint dislocation (9.8%). Hospital-acquired conditions, including surgical-site infection, urinary tract infection, deep vein thrombosis, and pulmonary embolism, accounted for 33% of all 30-day readmissions. Three independent risk factors for readmission were identified: revision surgery (odds ratio, 2.59), 3 or more comorbidities (odds ratio, 2.02), and extended length of stay (>4.3 days) during the index admission (odds ratio, 2.48). Other factors significantly (P < .05) associated with readmission were age over 75 years, dependent functional status, American Society of Anesthesiologists score of 4 or higher, cardiac comorbidity, 2 or more comorbidities, and urinary tract infection before discharge.