IMPORTANCE Thirty-day hospital readmissions have substantial direct costs and are increasingly used as a measure of quality care. However, data regarding the risk factors and reasons for readmissions in head and neck cancer surgery reconstruction are lacking. OBJECTIVE To describe the rate, risk factors, and causes of 30-day readmission in patients with head and neck cancer following free or pedicled flap reconstruction. DESIGN, SETTING, AND PARTICIPANTS This retrospective, population-based cohort study analyzed medical records from the Nationwide Readmissions Database of 9487 patients undergoing pedicled or free flap reconstruction of head and neck oncologic defects between January 1, 2010, and December 31, 2014. Data analysis was performed in October 2017. EXPOSURES Pedicled or free flap reconstruction of an oncologic head and neck defect. MAIN OUTCOMES AND MEASURES The primary outcome was 30-day all-cause readmissions. Secondary outcomes included risk factors, causes, and costs of readmission. Multivariate regression analyses were conducted to determine factors independently associated with 30-day readmissions. RESULTS Among 9487 patients included in the study (6798 male; 71.7%), the median age was 63 years (interquartile range, 55-71 years), and the 30-day readmission rate was 19.4% (n = 1839), with a mean cost per readmission of $15 916 (standard error of the mean, $785). The most common indication for readmission was wound complication (26.5%, n = 487). On multivariate regression, significant risk factors for 30-day readmission were median household income in the lowest quartile (vs highest quartile: odds ratio [