Fifty-three patients with non-Hodgkin's lymphoma of the breast were reviewed and classified using four current classifications of lymphoma. All patients were female with a mean age of 57 years. The majority of patients had histiocytic or large-cell lesions and presented as clinical Stage I. The tumors were described clinically as primary in the breast, and mammary parenchyma was found in 79% of the diagnostic biopsy specimens. The other specimens showed lymphoma in mammary adipose tissue. Survival was not influenced by the presence or absence of breast parenchyma in the biopsy. Statistically significant survival differences were found to be related to stage at presentation as well as to tumor grade, using Kiel and Working Formulation categories. Patients with Stage I disease and those with low-grade lesions had a more favorable prognosis. No discernible factors, including stage or histologic findings, appeared to affect the recurrence rate.