Rosai-Dorfman disease (RDD) is an idiopathic, benign proliferation of histiocytes that can be present in multiple organs such as lymph node, skin, soft tissue, orbit, central nerve system and bone; however, it rarely occurs in the breast. In general, RDD is a painless, fi rm and poorly defi ned lesion, which can radiologically mimic a breast cancer and is therefore an important differential consideration. The diagnosis of breast RDD is challenging, especially on a small biopsy specimen. We report a unique case of breast RDD with a literature review including common presentation, differential diagnosis, and recommended management. A high index of suspicion for this rare entity is essential to render a correct diagnosis, thereby avoiding unnecessary diagnostic tests and treatment.How to cite this article: Dai D, Cai Q, Vohra NA, Wong J, Therien ZP, et al. Rosai-Dorfman disease presenting as a breast mass. Arch Pathol Clin Res. 2019; 3: 008-014. https://dx.