Nevus comedonicus is a benign hamartoma of the pilosebaceous unit and is considered as a rare subtype of epidermal nevus. It was first described in 1895. It manifests as a group of closely dilated follicular openings with dark keratin plugs resembling comedones. Malignant degeneration of a nevus comedonicus is exceptional; we report a case of keratoacanthoma arising in extensive nevus comedonicus.