<p>Granulomatous mastitis (GM) is a rare, chronic, benign inflammatory breast disease with an unknown etiology, primarily affecting young women. It is often characterized by the presence of a painful mass, skin changes, and persistent inflammation, which can clinically resemble breast cancer. Due to the absence of specific imaging signatures and a poorly understood pathogenic mechanism, diagnosis is primarily achieved through exclusion. We present the case of a 31-year-old woman who, three years after undergoing a radical mastectomy for triple-negative breast cancer in her right breast, was diagnosed with GM in her left breast. The diagnosis was based on magnetic resonance imaging (MRI), conventional and contrast-enhanced ultrasound, and confirmed through histological analysis. The patient has experienced recurrent episodes of GM over the past three years. Notably, this case represents the first reported instance of granulomatous mastitis occurring in the contralateral breast following a radical mastectomy for breast cancer.</p>