Colony-site use by individually marked Caspian Terns (Sterna caspia) was studied at four breeding colonies in northeastern Lake Michigan during 1976-1979. I examined two related aspects of colony-site use: (1) colony-site preference in experienced breeders and (2) the relationship between reproductive success and colony-site tenacity. Terns showed a significant preference for the colony of previous breeding unless their preceding reproductive effort was unsuccessful. Caspian Terns tended to use the same colony site if young were produced but moved to a new location if reproductive success had been terminated or threatened at the traditional site.