Breast involvement by non-Hodgkin lymphomas is rare, and exceptional for T-cell lymphomas; we studied the morphologic, immunophenotypic, and clinical features of 11 patients with T-cell non-Hodgkin lymphomas involving the breast. Four cases fulfilled the definition criteria for primary breast lymphomas, 3 females and 1 male, with a median age of 51 years. One primary breast lymphomas was T-cell lymphoma unspecified, other was subcutaneous panniculitis-like T-cell lymphoma, and 2 cases were anaplastic large cell lymphomas. One of the anaplastic large cell lymphoma cases was found surrounding a silicone breast implant and presented as clinically as mastitis; whereas the other case occurred in a man. T-cell lymphoma secondarily involved the breast in 7 patients, all women and 1 bilateral, with a median age of 29 years. These secondary breast lymphomas occurred as part of widespread nodal or leukemic disease. Three patients had adult T-cell leukemia/lymphoma, including the patient with bilateral lesions, 3 others had precursor T-lymphoblastic lymphoma/leukemia, and the other presented with a peripheral-T-cell lymphoma non otherwise specified type. Breast T-cell lymphomas are very infrequent and are morphologically and clinically heterogeneous.