BACKGROUND: The recent intense attention to hospital readmissions and their implications for quality, safety, and reimbursement necessitates understanding specific subsets of readmitted patients. Frequently admitted patients, defined as patients who are admitted 5 or more times within 1 year, may have some distinguishing characteristics that require novel solutions. METHODS: A comprehensive administrative database (University HealthSystem Consortium's Clinical Data Base/Resource Manager™) was analyzed to identify demographic, social, and clinical characteristics of frequently admitted patients in 101 US academic medical centers. RESULTS: We studied 28,291 frequently admitted patients with 180,185 admissions over a 1-year period (2011-2012). These patients comprise 1.6% of all patients, but account for 8% of all admissions and 7% of direct costs. Their admissions are driven by multiple chronic conditions; compared to other hospitalized patients, they have significantly more comorbidities (an average of 7.1 vs 2.5), and 84% of their admissions are to medical services. A minority, but significantly more than other patients, have comorbidities of psychosis or substance abuse. Moreover, although they are slightly more likely than other patients to be on Medicaid or to be uninsured (27.6% vs 21.6%), nearly three-quarters have private or Medicare coverage. CONCLUSIONS: Patients who are frequently admitted to US academic medical centers are likely to have multiple complex chronic conditions and may have behavioral comorbidities that mediate their health behaviors, resulting in acute episodes requiring hospitalization. This information can be used to identify solutions for preventing repeat hospitalization for this small group of patients who consume a highly disproportionate share of healthcare resources.