The Renbök phenomenon, or reverse Koebner phenomenon, was first reported in 1991 by Happle et al,1 who described 4 patients with extensive alopecia areata of the scalp with hair growth within plaques of psoriasis. Three additional cases have subsequently been reported,2-4 and the term was later extended to include patients with mosaic phenomena, one with alopecia areata without a nevus flammeus, and another without a congenital nevus.5,6 Whereas the Koebner phenomenon involves psoriasis of traumatic or inflammatory origin, the Renbök phenomenon occurs when some inflammatory process is inhibited by psoriasis.