Granulomatous lobular mastitis is a rare chronic breast disease, firstly described by Kessler and Wolloch in 1972. In this article we present a 35-year-old patient with granulomatous lobular mastitis and in situ ductal carcinoma and discuss clinicopathological characteristics of the disease with literature data. A 35-year-old female patient admitted to the outpatient clinic with a complaint of swelling in right breast ongoing since March 2017. On the basis of physical examination and radiological examinations, antibiotic therapy was initiated considering the inflammatory breast disease and the patient was referred to our general surgery clinic because she did not benefit from treatment. On the recommendation of histopathological correlation, trucut biopsy was performed and reported as granulomatous mastitis. In the histopathological examination of the prepared sections, we found lobule-restricted, non-caseous granulomas and neoplastic epithelial cell proliferation in 4 different foci, the largest being 0.7x0.4 cm in diameter, limited to the ductal lobular system. The case was diagnosed as granulomatous lobular mastitis and in situ ductal carcinoma. This lesion, which clinically and radiologically can be confused with carcinoma, rarely coexists with breast carcinoma. Our case demonstrates the coexistence of granulomatous lobular mastitis and in situ ductal carcinoma.