• Following successful uniocular ptosis repair, measurable drooping of the fellow upper lid was noted in 11 (9.6%) of 115 cases. The original ptosis was due to a variety of causes. Methods of surgery included levator shortening, frontalis sling, and tarsoconjunctival resection. The droop of the eyelid not operated on was measured before and after ptosis surgery on the fellow eye. This contralateral phenomenon may be explained on the basis of Hering's law regarding yoke muscles. Surgical repair of the secondarily drooped lid was successful in five such cases.