A 71-year-old woman with a history of ovarian cancer presented to her previous doctor with an mass on her left thigh that had been increasing in size for the past three years. She was suspected of having sebaceous carcinoma on skin biopsy and was referred to our department. A red mass on the left thigh was excised and diagnosed as sebaceous carcinoma. One month later, a red mass on the right upper arm was excised and diagnosed as sebaceous adenoma. Immunohistochemical staining showed no expression of MSH2 and MSH6 in tumor cells, which led to suspicion of Muir-Torre syndrome. She was referred to the Gastroenterology department, where colonoscopy revealed cancer of the cecum and transverse colon. When multiple sebaceous tumors and their characteristic histopathological ndings are observed, screening for DNA mismatch repair protein deciency by immunohistochemical staining is necessary to diagnose Muir-Torre syndrome and detect concomitant malignant tumors in their early stages. Skin Research, 22 : 217-223, 2023