This report describes 8 cases of women who, when first examined, manifested metastatic mammary carcinoma in axillary lymph nodes. At mastectomy, the only demonstrable carcinoma was noninvasive (lobular, 4 patients; duct, 3 patients; duct and lobular, 1 patient) in so far as could be determined by means of light microscopic examination. In 2 cases treated more than five years ago, the patients were free of disease when last seen seven and 11 years postoperatively. It is possible that in these unusual cases, obscure foci of invasion were not found despite exhaustive histologic examination of the entire breast. Alternatively, metastases may have developed in the absence of invasion demonstrable by means of light microscopic examination. Results of electron microscopic studies as reported by others have documented extension of carcinoma cells through the basement membrane when this was not apparent in histologic sections. We have recently studied a series of patients with preinvasive breast carcinoma and observed metastatic breast carcinoma in axillary lymph nodes in 1% of these cases. The finding of carcinoma that appears histologically to be entirely preinvasive, whether duct or lobular in type, in a breast biopsy specimen does not entirely preclude the possibility of metastases in axillary lymph nodes.