A 3-month-old child is seen in clinic because of a rapidly enlarging birthmark on his back. On examination it is seen to be a strawberry naevus measuring 45×25 mm. The parents want to know how much further it will enlarge and when it is likely to settle. A straw poll of staff at grand round reveals that it is reckoned that maximum size should be achieved by 13 months (median) and resolution should have occurred in half the cases at 5 years (median).