Abstract: Primary granulocytic sarcoma (GS) is a rare entity, and even more unusual is the presence of primary GS of the breast. We describe such a case and report on the 19 cases of primary breast GS in the literature. Primary GS presents most commonly in skin and lymph nodes, therefore when it presents in the breast, misdiagnosis is a common problem. Primary breast GS is misdiagnosed most frequently as lymphoma or sarcoma. Histologic testing and immunostains are essential to provide the proper diagnosis. It appears that early initiation of systemic acute myelogenous leukemia (AML)-type chemotherapy is beneficial and may delay or avert the development of AML in bone marrow and blood.