Purpose: Bevacizumab is an antibody that binds vascular endothelial growth factor and has activity in metastatic renal cell carcinoma (RCC). Interferon alfa (IFN-α) is the historic standard initial treatment for RCC. A prospective, randomized, phase III trial of bevacizumab plus IFN-α versus IFN-α monotherapy was conducted. Patients and Methods: Patients with previously untreated, metastatic clear cell RCC were randomly assigned to receive either bevacizumab (10 mg/kg intravenously every 2 weeks) plus IFN-α (9 million units subcutaneously three times weekly) or the same dose and schedule of IFN-αmonotherapy in a multicenter phase III trial. The primary end point was overall survival (OS). Secondary end points were progression-free survival (PFS), objective response rate, and safety. Results: Seven hundred thirty-two patients were enrolled. The median OS time was 18.3 months (95% CI, 16.5 to 22.5 months) for bevacizumab plus IFN-αand 17.4 months (95% CI, 14.4 to 20.0 months) for IFN-α monotherapy (unstratified log-rank P = .097). Adjusting on stratification factors, the hazard ratio was 0.86 (95% CI, 0.73 to 1.01; stratified log-rank P = .069) favoring bevacizumab plus IFN-α. There was significantly more grade 3 to 4 hypertension (HTN), anorexia, fatigue, and proteinuria for bevacizumab plus IFN-α. Patients who developed HTN on bevacizumab plus IFN-α had a significantly improved PFS and OS versus patients without HTN. Conclusion OS favored the bevacizumab plus IFN-α arm but did not meet the predefined criteria for significance. HTN may be a biomarker of outcome with bevacizumab plus IFN-α.