BACKGROUND: Axillary dissection has maintained a role of primacy for the surgical therapy of invasive carcinoma of the breast for many years. More recently, early (T1) minimally invasive carcinoma of the breast has been diagnosed with increasing frequency, and the necessity of axillary dissection for sampling purposes in these small tumors has been questioned, based primarily on the finding of low rates of axillary metastases. STUDY DESIGN: The Rhode Island State Tumor Registry records of 1,126 patients with T1a or T1b tumors were examined to assess the effect of axillary dissection on patient outcome. These data span 9 years (1985 to 1992) with a median follow- up duration of 64 months. Five-year overall, disease-free, and breast cancer- specific (determinate) survival were determined according to treatment modality. Axillary node positivity was calculated for patients with minimally invasive carcinoma of the breast who underwent axillary dissection. Multivariate statistical methods were used to provide adjustment for known confounding prognostic variables. RESULTS: Omission of axillary dissection occurred in 157 cases and correlated with reductions in overall, disease- free, and breast cancer-specific survival (p<.001 in all cases). Nodal status significantly influenced disease-free survival in minimally invasive carcinoma of the breast (90 percent node-negative compared with 76 percent node-positive, p=.02). Nodal positivity was evident in 18.2 percent of patients undergoing axillary dissection for minimally invasive carcinoma of the breast (9.8 percent for T1a, 19.4 percent for T1b, p=.01). In multivariate analysis, the performance of axillary dissection with breast conservation or modified radical mastectomy were independent predictors of overall survival, as well as disease-free and breast cancer-specific survival. CONCLUSIONS: A significant number of patients with small (less than or equal to 1 cm) invasive tumors of the breast will have axillary metastases at the time of diagnosis. Omission of axillary dissection in these patients was associated with significant impairment of overall, disease-free, and breast cancer-specific survival. Axillary dissection should continue to be a standard approach for the surgical therapy of all patients with invasive carcinoma of the breast, regardless of tumor size.