Eccrine porocarcinoma is a rare malignant tumor arising from the intraepidermal ductal portion of the eccrine sweat gland. Seborrheic keratosis is a common epithelial tumor in elderly patients; it is not considered to be precancerous. We report a case of eccrine porocarcinoma associated with seborrheic keratosis in a 69-year-old male. Such a case has not been reported in Korean dermatologic literature. Although reports of seborrheic keratosis transforming into a sweat gland tumor are rare in worldwide literature, the present case suggests that seborrheic keratosis may develop into malignant sweat gland tumors. (Korean J Dermatol 2000; 39(1): 101-103)