The damaging effects of ear tags used to identify sheep were studied by examining the ears of sheep after slaughter in three different abattoirs and the ears of sheep on a farm. In total, 1040 ears with tags were examined. There were six types of ear tag: metal 'Ketchum' style loop tags; two-piece rigid plastic tags; 'AlIflex' style flexible plastic tags with a male and female part; golf tee-shaped plastic ear tags; one-piece rigid plastic loop tags; and one-piece flexible plastic tags with a flap. The metal loop tags and plastic loop tags caused the most lesions, and the majority of the severe lesions. Ear tags placed near to the tip of the ear appeared to cause more damage. Some of the Ketchum style metal tags and two-piece rigid plastic tags appeared to be relatively new, as if recently fitted. These tags were more often associated with ear lesions, particularly moderate or severe lesions. The AlIflex style flexible plastic tags caused the fewest problems, and the golf tee-shaped plastic tags also caused significantly fewer problems than the other tags.