Porokeratosis is a disorder of epidermal keratinization. A 27-year-old woman had papular, linearly arranged, hyperkeratotic lesions on the right foot since birth. Over the course of her life, the lesions progressed to involve the entire right leg and extended to the right side of her trunk, the right arm and chin. The clinical diagnosis of unilateral linear porokeratosis was confirmed by histopathology.