Background: Hospital readmissions following surgery are a focus of quality improvement efforts nationwide. Although some reflect appropriate care, others are potentially preventable readmissions (PPRs). We aim to describe the burden, timing, and factors associated with PPRs after complex cancer surgery. Methods: The National Readmissions Dataset (2013) was used to select patients undergoing a complex oncologic resection (defined as esophagectomy/gastrectomy, hepatectomy, pancreatectomy, colorectal resection, lung resection, and cystectomy). All Readmissions occurring within 30 days from discharge were analyzed. Causes for readmissions were categorized in eleven diagnostic groups and tabulated. ICD-9 primary diagnosis codes were reviewed to identify PPRs. Logistic regression analyses were used to identify demographic, clinical and hospital factors associated with PPRs. Results: We analyzed 60,970 patients with 92,260 admissions. A 30 day readmission occurred in 14% of patients, and was highest following cystectomy (25%) and lowest for lung resections (9%). Of all readmissions 82% were deemed to be PPRs. Half of PPRs occurred within the first 10 days of discharge. Infections, gastrointestinal complications and respiratory conditions accounted for 59% of PPRs. Other common causes included dehydration/electrolyte deficiencies (11%), exacerbation of comorbidity (9.2%), bleeding (5%), thromboembolism (3.5%), and wound complications (3.2%). Factors associated with an increased likelihood of PPRs include Medicaid compared with private insurance (OR 1.24, 95%CI 0.8-1.7), higher comorbid conditions (OR 1.44, 95%CI 1.32, 1.59), and discharge to a facility (OR 1.9, 95%CI 1.7-2.1). Patients with a prolonged hospital stay or a major complication during the index admission had a 34% (OR 1.34, 95%CI 1.3-1.4), and 64% (OR 1.64, 95%CI 1.5-1.7) higher likelihood of a PPR respectively. Conclusions: Most 30 day readmissions after complex cancer surgery are potentially preventable and occur within 10 days of discharge. We identify common causes of readmission and high risk populations to help physicians, administrators and policy makers develop strategies to decrease PPRs.