The aim of the study was to examine the temporal readmission pattern, proportion of readmissions attributed to cardiovascular (CV) causes, and the duration and costs associated with readmission in hospitalized patients with atrial fibrillation/flutter (AF/AFL). This retrospective cohort study used medical claims data from the PharMetrics Patient-Centric database (IMS Health, Watertown, MA) between January 2007 and March 2008. The patients hospitalized with a primary diagnosis of AF/AFL and with ≥12 months' continuous medical and prescription coverage before and after the initial AF/AFL hospitalization were identified from this database. The main outcome measures were rehospitalization patterns [all-cause, all CV-related (including AF/AFL), and AF/AFL-related only], which were assessed over the 12-month post-index period, and costs of initial and subsequent AF/AFL-related hospitalizations that were compared. The study included 8035 patients with AF/AFL (mean age 66.1 years; 57.6% males). Rehospitalization was common (37.9% of patients), with the most frequent causes being CV (34.1%) and, specifically, AF/AFL-related (26.8%). The highest proportion of rehospitalizations occurred within 30 days of the initial hospitalization (25%). Readmissions with a primary diagnosis of AF/AFL (n = 1238) were significantly longer (4.0 vs. 3.6 days; P = 0.0229) and more costly (US$8966 vs. US$7080; P < 0.0001) than the index hospitalization. Hospitalized AF/AFL patients experience high rates of CV- and AF/AFL-related readmissions, particularly within the first 30 days. Subsequent AF/AFL-related readmissions incur higher costs than the initial AF/AFL hospitalization. Treatments resulting in reduced readmissions would improve patient outcomes, quality of life and the cost burden associated with AF/AFL.