Reticulated acanthoma with sebaceous differentiation (RASD) is characterized by the reticulated proliferation of spinous cells with aggregates of mature sebocytes in the bases of the strands of the keratinocytes, often linking rete ridges. Here, we report the first case reported as RASD. A 55-year-old woman presented with a 15-year history of a slightly pruritic patch on the upper back, and the histology was typical for RASD. She had been bothered by a yellow discharge from the tumor. Skin tumors with sebaceous differentiation are occasionally associated with Muir-Torre syndrome. However, immunohistochemical staining for mutS homolog 2 (MSH-2) and mutL homolog 1 (MLH-1) showed positive staining within the nuclei of sebaceous cells and cells in the dermis. Therefore, it is most likely that the present case is not associated with Muir-Torre syndrome.