Granulomatous lobular mastitis is a rare chronic inflammatory disease that has clinical and radiologic findings similar to those of breast cancer. We performed a retrospective analysis of clinical, imaging, and treatment findings in 54 women diagnosed with granulomatous lobular mastitis between January 2000 and April 2008. The imaging findings of granulomatous lobular mastitis overlap with those of malignancy. The most common presentation is a focal asymmetric density on mammography and an irregular hypoechoic mass with tubular extensions on ultrasound. Core biopsy is typically diagnostic. Once the diagnosis is established by tissue sampling, corticosteroids are the first line of treatment.