Eccrine syringofibroadenoma (ESFA) is a rare, benign adnexal neoplasm which usually manifests as a solitary nodule on the extremities of elderly patients. Few case reports have described an association between ESFA and carcinomas including squamous cell carcinoma, porocarcinoma, and basal cell carcinoma. A 66-year-old male presented with a pruritic, erythematous brownish solitary plaque with crusted and verrucous surface on the extensor side of the right thigh. The lesion developed 6 to 7 years ago, and had been growing slowly. Biopsy revealed anastomosing epithelial strands which were composed of 2 areas: the upper area consisting of dysplastic cells with prominent nucleoli and abundant mitoses, and the lower area consisting of oval and round cells, and occasionally small luminal ducts. Dysplastic cells comprised almost the entire epidermis but did not invade into the dermis. Benign syringofibroadenomatous lesion surrounded the dysplastic cells in the lowermost portion of the epidermis. Although it is still unclear whether ESFA undergoes malignant transformation or it is a reactive change to carcinoma, complete excision should be performed to prevent malignant transformation with unknown risk. (Ann Dermatol 32(1) 57∼63, 2020)