The objective of this phase I/II study was to establish the recommended dose of biweekly vinorelbine and oxaliplatin in patients with metastatic breast cancer and to evaluate the efficacy and safety profile of this schedule as first-line treatment. Four different dose levels of vinorelbine and oxaliplatin were selected for the phase I study: (i) 25 and 80 mg/m²; (ii) 25 and 90 mg/m²; (iii) 25 and 100 mg/m²; and (iv) 30 and 90 mg/m²; respectively. At least three patients were treated at each dose level. Overall, 12 patients were included in the phase I trial. No dose-limiting toxicities occurred at any dose level. Therefore, the fourth dose level (30 mg/m² of vinorelbine and 90 mg/m² of oxaliplatin) every 2 weeks was selected for the phase II trial. In this part, 44 patients were included and 61% completed the eight 2-week cycles of study treatment. On an intention-to-treat basis, overall response rate was 59%, and median progression-free survival and overall survival were 9.2 months (95% confidence interval: 7.6-10.9) and 18.6 months (95% confidence interval: 14.4-22.9), respectively. The main severe toxicities were neutropenia (46%) and fatigue (14%). We conclude that the biweekly combination of vinorelbine and oxaliplatin at doses of 30 mg/m² and 90 mg/m², respectively, is highly active and well tolerated as first-line treatment for patients with metastatic breast cancer.