Muir-Torre syndrome is defined by concurrent or sequential development of internal malignancy - most commonly colorectal cancer - and sebaceous neoplasm or multiple keratoacanthomas. Recent studies revealed it was caused by mutations in DNA mismatch repair genes, and suggested screening for mismatch repair gene defects may be of value for patients with Muir-Torre syndrome. We, herein, report a patient with Muir-Torre syndrome, who developed breast cancer and extra-ocular sebaceous carcinoma. In addition, we discussed our experience of immunohistochemical staining for mismatch repair protein with a review of the literature. (Korean J Dermatol 2010;48(8):696~699)