BACKGROUND Some authors have stated the undesirability of axillary lymph node dissections for very small breast cancers, because so few of their patients have lymph node metastases (3% for T1a lesions in one series). METHODS Of 6,308 breast cancer cases reviewed from three large urban hospitals 3,077 single primary cases with both axillary dissection and accurate tumor measurements were statistically analyzed. RESULTS For T1a lesions we found axillary metastases to be four times higher (12%) than others have reported. For each tumor size there was a statistically significant difference in the percentage of axillary metastases. There was also a statistically significant difference in the breast cancer-specific survival of patients with different tumor sizes (n = 3,077) at the 3-year, 5-year, 7-year, and 10-year periods. CONCLUSIONS These results justify axillary node dissections even for very small invasive cancers of the breast, particularly for invasive ductal histology.