Interest is growing in preventing readmissions as payers start to link reimbursement to readmission rates. The purpose of this study was to assess factors contributing to 30-day readmission for patients undergoing gastric bypass (GB) and determine whether these readmissions may be preventable. Data were from the Pennsylvania Health Care Cost Containment Council (PHC4) and included all patients undergoing elective GB for obesity in 2011 (n = 4427). The outcomes measured were length of stay (LOS) and 30-day readmission. Univariate comparisons between characteristics of readmitted (n = 298) and non-readmitted (n = 4133) patients were performed. Readmission was modeled using multivariate logistic regression; LOS was modeled using linear regression. Of the 298 (6.6%) patients who were readmitted, the most common causes for readmission were bleeding (11.84%), infection (8.88%), and abdominal pain (7.89%). In multivariate analyses, black race, open GB, and history of myocardial infarction or rheumatoid arthritis were associated with increased odds of readmission. Longer LOS was also predictive of readmission (OR 1.10, p = <0.0001). Patients who were >50 years old and those with history of congestive heart failure, peripheral vascular, and kidney diseases were more likely to have longer LOS. Black race, open surgery, and discharge to an extended care facility were also predictive of prolonged LOS. The most common causes of readmission following elective GB were bleeding, infection, and abdominal pain. Since several patient-specific factors were associated with higher odds of readmission and longer LOS, there are opportunities to design interventions to prevent readmissions and decrease LOS in this patient population.