INTRODUCTION: To assess risk factors for unplanned readmission following open and minimally invasive partial nephrectomy (PN). MATERIALS AND METHODS: From the National Surgical Quality Improvement Program database, patients with renal malignancy undergoing PN in 2011 or 2012 were reviewed. Using multivariable logistic regression, we identified variables associated with 30 day hospital readmission. RESULTS: Of the 2124 patients identified who underwent PN, 1253 (59%) were minimally invasive PN (MIPN) and 871 (41%) open PN (OPN). There were no differences in preoperative comorbidities between MIPN and OPN patients. The rate of unplanned hospital readmission for the entire cohort was 5%, which varied from 7% for OPN to 4% for MIPN. Seven percent of OPN and 2% of MIPN patients developed a Clavien grade III-V complication. For OPN, developing an in-hospital Clavien grade III-V complication was associated with a 6-fold increase in the odds of requiring subsequent readmission (95% CI 2.22-14.47, p < 0.001). For MIPN, an in-hospital Clavien grade III-V complication was associated with nearly 16 times increased odds of unplanned readmission (95% CI 6.08-41.65, p<0.001) and history of chronic anticoagulation was associated with a five times increased odds of unplanned readmission (95% CI 1.44-18.25, p = 0.012). Finally, operative time for MIPN was associated with increased odds of readmission (OR 1.08, 95% CI 1.04-1.16, p < 0.001). Patient comorbidities and ASA score were not associated with unplanned readmission for OPN or MIPN. CONCLUSIONS: Patients developing high grade complications are at increased risk of subsequent unplanned readmission. These patients who develop significant in-hospital complications may benefit from increased post-discharge contact with healthcare providers and from preoperative counseling regarding their risk of unplanned readmission.