Diabetic fibrous mastopathy (DFM) is a relatively rare condition that most often occurs in insulin-dependent diabetics with a characteristic hypoechoic appearance on ultrasound (US). DFM frequently poses a diagnostic challenge in radiology due to malignant imaging similarities, and core needle biopsy is often required. If DFM is in the differential, fine-needle aspiration should not be considered as it will likely be non-diagnostic due to insufficient sampling and excisional biopsy should be avoided as it may worsen the disease process. Therefore, high clinical suspicion of DFM is important for diagnostic intervention consideration. We report the case of a 57-year-old who presented with a firm breast lump which on mammography was seen as a new 5.8 by 5.3 cm global asymmetry. US was performed and a diffuse area of increased echogenicity without posterior shadowing was identified. Given the appearance and patient history, DFM was considered unlikely. However, core needle biopsy revealed diabetic lymphocytic mastopathy consistent with DFM. Even though DFM is uncommon and has been reported to have a specific US appearance, it should be included in the differential for a palpable breast lump in any diabetic patient regardless of glucose control or atypical imaging findings.