Nevus unius lateris (NUL) is a variant of an epidermal nevus that involves a widespread body surface, especially half of the body, and its onset usually occurs at birth or early life. An increased risk of basal cell carcinoma (BCC) in epidermal nevus has also been reported. However, the exact incidence remains unknown. A 67-year-old female patient visited our dermatology clinic with black nodules protruding over multiple verrucous brownish patches and plaques on the right side of the trunk. The patient had congenital NUL. Black nodules were observed to develop several months previously and gradually enlarged. The skin biopsy of one black nodule was consistent with BCC. Subsequently, Mohs micrographic surgery was performed for the BCC. To date, there have been few reports of BCC arising within the nevus unius lateri. Herein, we report a rare case of BCC considered to originate from a congenital NUL. (Korean J Dermatol 2024;62(1):50∼52)