BACKGROUND & AIMS: Old age must be considered in weighing the risks of complications vs benefits of treatment for patients with inflammatory bowel diseases (IBD). We conducted a nationally representative cohort study to estimate the independent effects of frailty on burden, costs, and causes for hospitalization in patients with IBD. METHODS: We searched the Nationwide Readmissions Database to identify 47,402 patients with IBD, hospitalized from January through June 2013 and followed for readmission through December 31, 2013. Based on a validated hospital frailty risk scoring system, 15,507 patients were considered frail and 31,895 were considered non-frail at index admission. We evaluated the independent effect of frailty on longitudinal burden and costs of hospitalization, inpatient mortality, risk of readmission and surgery, and reasons for readmission. RESULTS: Over a median follow-up time of 10 months, adjusting for age, sex, income, comorbidity index, depression, obesity, severity, and indication for index hospitalization, frailty was independently associated with 57% higher risk of mortality (adjusted hazard ratio [aHR], 1.57; 95% CI, 1.34-1.83), 21% higher risk of all-cause readmission (adjusted hazard ratio [HR], 1.21; 95% CI, 1.17-1.25), and 22% higher risk of readmission for severe IBD (aHR, 1.22; 95% CI, 1.16-1.29). Frail patients with IBD spent more days in the hospital annually (median 9 days; interquartile range, 4-18 days vs median 5 days for non-frail patients; interquartile range, 3-10 days; P < .01) with higher costs of hospitalization ($17,791; interquartile range, $8368-$38,942 vs $10,924 for non-frail patients, interquartile range, $5571-$22,632; P < .01). Infections, rather than IBD, were the leading cause of hospitalization for frail patients. CONCLUSIONS: Frailty is independently associated with higher mortality and burden of hospitalization in patients with IBD; infections are the leading cause of hospitalization. Frailty should be considered in treatment approach, especially in older patients with IBD.