IMPORTANCE Readmissions after surgery are costly and may reflect quality of care in the index hospitalization. OBJECTIVES To determine the timing of postoperative complications with respect to hospital discharge and the frequency of readmission stratified by predischarge and postdischarge occurrence of complications. DESIGN, SETTING, AND PARTICIPANTS This is a retrospective cohort study of national Veterans Affairs Surgical Quality Improvement Program preoperative risk and outcome data on the Surgical Care Improvement Project cohort for operations performed from January 2005 to August 2009, including colorectal, arthroplasty, vascular, and gynecologic procedures. The association between timing of complication with respect to index hospitalization and 30-day readmission was modeled using generalized estimating equations. MAIN OUTCOME AND MEASURE All-cause readmission within 30 days of the index surgical hospitalization discharge. RESULTS Our study of 59 273 surgical procedures performed at 112 Department of Veterans Affairs (VA) hospitals found an overall complication rate of 22.6%(predischarge complications, 71.9%; postdischarge complications, 28.1%). The proportion of postdischarge complications varied significantly, from 8.7%for respiratory complications to 55.7%for surgical site infection (P > .001). The overall 30-day readmission rate was 11.9%, of which only 56.0%of readmissions were associated with a currently assessed complication. Readmission was predicted by patient comorbid conditions, procedure factors, and the occurrence of postoperative complications. Multivariable generalized estimating equation models of readmission adjusting for patient and procedure characteristics, hospital, and index length of stay found that the occurrence of postdischarge complications had the highest odds of readmission (odds ratio, 7.4-20.8) compared with predischarge complications (odds ratio, 0.9-1.48). CONCLUSIONS AND RELEVANCE More than one-quarter of assessed complications are diagnosed after hospital discharge and strongly predict readmission. Hospital discharge is an insufficient end point for quality assessment. Although readmission is associated with complications, almost half of readmissions are not associated with a complication currently assessed by the Veterans Affairs Surgical Quality Improvement Program. © 2014 American Medical Association.