We report three cases of bilateral malignant lymphoma of the breast in patients with a familial history of cancers. All the patients had B-cell malignant lymphoma and were treated by a radical mastectomy and polychemotherapy. Bilateral tumors were detected synchronously in one case, whereas the second tumors in the other cases occurred 4 years and 8 years after the initial treatment. Although the patients had no relevant past history, these cases were notable for the fact that all were associated with a familial history of cancers. One patient had a definite familial history of breast cancer, that is to say, her mother, sister and brother all suffered from this disease. The brother of another patient died of gastric cancer while two of her uncles each suffered from sarcoma of the lower extremities and a brain tumor, respectively. As for the remaining patient, one of her maternal uncles and an aunt also died of prostate cancer and leukemia, respectively. However, only one out of seven patients with unilateral malignant lymphoma of the breast used for comparison had a familial history of cancer. A possible relationship between bilateral primary malignant lymphoma of the breast and a familial history of cancer is suggested.