Basaloid carcinoma of the breast (BCB) is an unusual neoplasm composed of basal-type neoplastic cells similar to those found in adenoid cystic carcinoma (ACC), although lacking distinctive features such as a cribriform pattern, a dual neoplastic population (epithelial-myoepithelial/basaloid), and stromal deposits of basement membrane-like material. In this article, we present 9 cases of breast cancer showing overall/predominant basaloid morphology. Patients' ages ranged from 47 to 75 years (mean, 61.4 years). Surgical treatment included mastectomy or quadrant excision with or without axillary dissection. Most tumors had a circumscribed outline and ranged in size from 1.3 to 5.5 cm (mean, 2.5 cm). Microscopically, they featured sheets, nests, and cords of proliferating basaloid tumor cells with ovoid, hyperchromatic nuclei with inconspicuous nucleoli and scant cytoplasm. No foci with characteristics of ACC were found in any of the tumors. Transition into pleomorphic basaloid carcinoma with foci of high-grade ductal carcinoma in situ plus infiltrating ductal carcinoma (IDC) and admixture with grade 3 ductal and sarcomatoid carcinoma was seen in 2 cases. Tumor cells were positive for wide-spectrum keratins and epithelial membrane antigen (9/9) and high-molecular-weight keratins (7/9). They were negative for smooth muscle actin, p63, calponin, and CD10 in all tested cases. Estrogen receptor, progesterone receptor, and HER-2 were negative. Axillary lymph node metastases were seen in 3 cases. At follow-up (range, 10-169 months), 5 patients were alive, 1 with evidence of contralateral breast cancer. Three patients died: one of disseminated BCB metastases, another of liver cirrhosis, and one of disseminated estrogen receptor/progesterone receptor-positive contralateral IDC. One patient was lost to follow-up. We concluded that BCB has some phenotypic and immunohistochemical features enabling its distinction from ACC or IDC. It appears to be a morphological and possibly a clinical entity. Compared with ACC, BCB appears to be more aggressive and may entail a more guarded prognosis.