A man in his 40s presented with a 10-year history of pruritic perianal eruption and hyperkeratotic plaques involving his intergluteal cleft and buttocks, which had gradually become more extensive and verrucous (Figure, A). There was no history of other skin problems; he took no medications and was in good health. Histological examination revealed multiple cornoid lamellae and intense hyperkeratosis (Figure, B). Beneath the cornoid lamellae, the granular layer was absent, and there were some dyskeratotic cells. A diagnosis of porokeratosis ptychotropica was made based on the clinical appearance and typical histological manifestations. The patient was treated with topical retinoid creams and oral acitretin, but the lesions only slightly improved during 3 months’ follow-up.