Diabetic mastopathy is an uncommon, benign breast lesion that is typically seen in patients with type 1 diabetes mellitus (T1DM). The main differential diagnosis for diabetic mastopathy is breast carcinoma, which appears similarly on clinical examination and diagnostic imaging. Although the etiology of diabetic mastopathy is poorly understood, it has been associated with several autoimmune conditions, such as Hashimoto’s thyroiditis, systemic lupus erythematosus, and Sjogren’s syndrome. Here, we report a case of diabetic mastopathy in a T1DM patient with an associated history of elevated thyroid peroxidase (TPO) and antimitochondrial antibody (AMA) levels, giving further support to the theory of autoimmune etiopathogenesis.