BACKGROUND: In a phase 3 trial comparing the efficacy and safety of axitinib versus sorafenib as second-line treatment for metastatic renal cell carcinoma, patients given axitinib had a longer progression-free survival (PFS). Here, we report overall survival and updated efficacy, quality of life, and safety results. METHODS: Eligible patients had clear cell metastatic renal cell carcinoma, progressive disease after one approved systemic treatment, and an Eastern Cooperative Oncology Group performance status (ECOG PS) of 0-1. 723 patients were stratified by ECOG PS and previous treatment and randomly allocated (1:1) to receive axitinib (5 mg twice daily; n=361) or sorafenib (400 mg twice daily; n=362). The primary endpoint was PFS assessed by a masked, independent radiology review committee. We assessed patient-reported outcomes using validated questionnaires. Baseline characteristics and development of hypertension on treatment were studied as prognostic factors. Efficacy was assessed in the intention-to-treat population, and safety was assessed in patients who received at least one dose of the study drug. This ongoing trial is registered on ClinicalTrials.gov, number NCT00678392. FINDINGS: Median overall survival was 20.1 months (95% CI 16.7-23.4) with axitinib and 19.2 months (17.5-22.3) with sorafenib (hazard ratio [HR] 0.969, 95% CI 0.800-1.174; one-sided p=0.3744). Median investigator-assessed PFS was 8.3 months (95% CI 6.7-9.2) with axitinib and 5·7 months (4.7-6.5) with sorafenib (HR 0.656, 95% CI 0.552-0.779; one-sided p<0.0001). Patient-reported outcomes scores were similar in the treatment groups at baseline, were maintained during treatment, but decreased at end-of-treatment. Common grade 3 or higher treatment-related adverse events were hypertension (60 [17%]), diarrhoea (40 [11%]), and fatigue (37 [10%]) in 359 axitinib-treated patients and hand-foot syndrome (61 [17%]), hypertension (43 [12%]), and diarrhoea (27 [8%]) in 355 sorafenib-treated patients. In a post-hoc 12-week landmark analysis, median overall survival was longer in patients with a diastolic blood pressure of 90 mm Hg or greater than in those with a diastolic blood pressure of less than 90 mm Hg: 20.7 months (95% CI 18.4-24.6) versus 12.9 months (10.1-20.4) in the axitinib group (p=0.0116), and 20.2 months (17.1-32.0) versus 14.8 months (12.0-17.7) in the sorafenib group (one-sided p=0.0020). INTERPRETATION: Although overall survival, a secondary endpoint for the study, did not differ between the two groups, investigator-assessed PFS remained longer in the axitinib group compared with the sorafenib group. These results establish axitinib as a second-line treatment option for patients with metastatic renal cell carcinoma. FUNDING: Pfizer Inc.