A vascular malformation of developmental origin characterized pathologically by ectasia of superficial dermal capillaries, and clinically by persistent macular erythema. In the past, port wine stains have frequently been termed capillary hemangiomas, which they are not; unfortunately this confusing practice persists: HEMANGIOMA, CAPILLARY is neoplastic, a port-wine stain is non-neoplastic. Port-wine stains vary in color from fairly pale pink to deep red or purple and in size from a few millimeters to many centimeters in diameter. The face is the most frequently affected site and they are most often unilateral. (From Rook et al., Textbook of Dermatology, 5th ed, p483)