The authors describe 10 cases of malignant non-Hodgkin's lymphoma in a mammary site in women aged 38 to 82 years. The clinical examination and the sometimes suggest an adenocarcinomatous lesion, thus leading to a useless surgical exeresis. An initial histological study provides the diagnosis. A complete assessment of extension allows an accurate staging and the refinement of the therapeutic schedule. Exclusive radiation therapy seems to be justified in low-malignancy forms remaining strictly confined to the breast. For the high- and medium-malignancy forms, the essential weapon is chemotherapy, which seems to improve the duration and rate of remission.