Primary malignant lymphomas of the breast are uncommon findings, representing 0.12% to 0.53% of all breast cancers. Secondary lymphomas are also uncommon, but they make the most frequent metastatic breast cancers. From January 1989 through December 1992, at the Department of Radiology of the University of Perugia, the authors observed 6 cases of breast lymphoma--1 primary and 5 secondary lesions--in women 52 to 67 years old (average 60 years). The only primary lymphoma was unilateral, multiple and localized on the right side; the secondary ones were diffuse and bilateral in 4 cases and unilateral and nodular in 1 case. The clinical findings were always suggestive of a malignant lesion and so were the mammographic and US findings in 4 diffuse lesions--3 bilateral and 1 unilateral cancers; in both the primary lymphoma and the secondary nodular lymphoma mammography showed benign patterns. Diagnosis was made in all cases following biopsy or resection of the breast mass; all the lymphomas were of the non-Hodgkin's type. The authors report on the major clinical, mammographic and US features of this unusual disease and include a short review of the relative literature.