We analyzed the age at diagnosis and the tumor size as determinants of axillary node involvement in 725 consecutive patients with breast cancer. The prevalence of nodal involvement increased consistently with tumor diameter from 18.9% in tumors smaller than 10 mm to 72.9% in those measuring 40 mm, or more. The risk also varied with age, the lowest prevalence being found in the youngest and the oldest patients and the highest one in the 40–59-year age group. When analyzed as a continuous variable age was best fitted as a second order term and it was a statistically significant (p = 0.04) determinant of axillary metastases in a multivariate model where tumor diameter, histopathological classification and estrogen receptor concentration were taken into account as possible confounding variables. The findings indicate that the parallelism between the establishment of metastases in lymph nodes and at distant sites may vary with age. The prognostic value of nodal status may therefore depend on age at diagnosis.