Adenoid cystic carcinoma (ACC) is a rare malignant tumor of the breast that occurs in <0.1% of all patients diagnosed with breast cancer. The mean patient age at the time of diagnosis is 50-60 years. Typically, the tumor presents as a subareolar mass or as pain in the breast. While the radiological appearances of ACC are generally non-specific, the diagnosis can be made on fine-needle aspiration cytology. In the present study, a 58-year-old female patient was admitted to the Department of Radiation Oncology (Karadeniz Technical University, Faculty of Medicine, Trabzon, Turkey) with complaints of pain in the upper outer quadrant of the right breast. An excision biopsy of a lump in the upper outer quadrant revealed ACC, and perineural invasion was present. Subsequently, the patient underwent breast conservation surgery and sentinel lymph node dissection. Pathology from the second surgery depicted ACC in the form of microscopic foci around the initial surgical cavity, with two reactive sentinel lymph nodes and the closest negative margin at 2 mm. The patient was treated with radiotherapy following the surgery. No recurrence and metastasis were found after 20 months of follow-up. In conclusion, mammary ACC is a rare malignant neoplasm of the breast. Although surgery is the main treatment, the optimal adjuvant treatment of ACC of the breast has not yet been determined due to its low incidence.