BACKGROUND: Granulomatous lobular mastitis (GLM) is an inflammatory disease of the breast, which can mimic breast cancer in clinical and radiological findings. We conducted the present study in order to determine the diagnostic and other important aspects of this disease. METHODS: In this study, we reviewed the records of 38 patients with granulomatous lobular mastitis in order to describe the clinical, imaging, laboratory, pathologic, and treatment aspects of this disease. RESULTS: All of the patients’ ages were in the range of 22-62 years (mean age: 42 years). All of them had children, history of oral contraceptive pill (OCP) usage, antibiotic therapy and mammoplasty. In physical examination, dimpling, edema, inflammation, ulcer, abscess, and firm mass were detected. Size of masses was in the range of 2 × 2 to 8 × 6 cm and their location, in most cases, was in the superior lateral quadrant or central region. In Ultrasonography, a hypoechoic fibroglandular mass and collection, and in pathologic findings, granulomatous reaction was reported. These patients were treated by antibiotics, corticosteroids, and surgery. CONCLUSIONS: GLM is a chronic inflammatory lesion of the breast which can mimic breast cancer. A history of child bearing, lactation, and OCP drug usage have suspicious roles in the formation of GLM. The most common clinical sign in these patients is a painful mass in the breast. We uncovered that clinical and radiological findings are not specific and sufficient for diagnosis of GLM. Therefore, for better diagnosis of this disease, usage of core, incisional, or excisional biopsy are recommended.