We investigated whether increasing size of lymph nodes (LN) metastases is associated with lower breast cancer-specific survival (BCSS) and overall survival (OS) independent of the number of positive LNs. Using Surveillance, Epidemiology, and End Results registry data, we identified 8791 women diagnosed between 1990 and 2003 with node-positive, non-metastatic invasive breast cancer treated with surgery and axillary LN dissection. Size of the largest involved LN metastasis was categorized as ≤2 mm, >2 mm to <2 cm, and ≥2 cm. BCSS and OS were estimated using the Kaplan-Meier method and compared using log-rank statistics. Adjusted hazard ratios (HR) were calculated using Cox proportional hazards models. Median follow-up was 109 months. Largest LN size was ≤2 mm, >2 mm to <2 cm, and ≥2 cm in 2219 (25.2 %), 5047 (57.4 %), and 1525 (17.3 %) women, respectively. The 10-year BCSS for women with LNs ≤2 mm, >2 mm to <2 cm, and ≥2 cm was 82.9, 75.5, 64.8 %, respectively (p < 0.001). On multivariable analysis, large (≥2 cm) LN size was significantly associated with worsened BCSS (HR: 1.169; p = 0.026) and OS (HR: 1.169; p = 0.006) in addition to age, race, grade, PR status, adjuvant radiation, T-stage, and number of positive LNs. Large (≥2 cm) LNs metastases were associated with lower BCSS and OS after controlling for other known prognostic factors including number of positive LNs. LN size could be useful to risk-stratify patients for adjuvant therapy if these results are validated in future prospective studies.