Lymphoma of the breast is unusual, and synchronous bilateral lymphoma and carcinoma of the breast is extremely rare. We present the case of a 51-year-old woman who found a mass in her left breast. Ultrasound scan findings revealed nodules at the 2 o'clock position in her left breast and focal dilation of the duct at the 8-9 o'clock and 10 o'clock position in her right and left breasts, respectively. A left breast ultrasound-guided core needle biopsy and right breast segmental excisional biopsy were performed. Pathological and immunohistochemical examination revealed left breast invasive ductal carcinoma and right breast diffuse large B-cell lymphoma of the non-germinal center type. Pathological examination of the left breast modified radical mastectomy specimen revealed synchronous invasive ductal carcinoma (grade III) and diffuse large B-cell lymphoma. The patient received chemotherapy and bone marrow transplantation in another hospital. Based on a review of the relevant literature, we discuss the diagnosis, clinical features, treatment, and prognosis of synchronous breast lymphoma and invasive ductal carcinoma.