We analysed 1,126 recoveries of Caspain Terns (Sterna caspia) from 1 January 1962 to 30 June 1986. Birds had been banded in their hatching year at colonies in the Great Lakes from 1959 to 1982. Adults (age .gtoreq. 2.5 years) summer on the Great Lakes in June and July, winter in the southern Atlantic and Gulf Coast states and the Caribbean Basin from November to March, and migrate, between their summer and winter ranges in April-May and August-October. Juveniles (age 0-6 months) use the same migration routes as adults i.e. the American Atlantic Coast and possibly the Mississippi Flyway, and winter in the same areas as adults. Immatures (age 6-18 months) apparently spend all four seasons on the adult winter range. Recoveries of sub-adults (age 18-30 months) during June and July included both the Great Lakes and the adult winter range while recoveries in other seasons were similar to those of adults but also included areas not normally associated with Great Lakes'' Caspian Terns. We suggest that sub-adults have a greater tendency to wander than the three other age groups. We analysed interchanges of adults among the Great Lakes region and the two other major banding regions (> 5000 chicks banded) in North America as well as interchanges as adults among individual lakes of the Great Lakes and among 10'' X 10'' blocks were birds had been banded. Great Lakes'' birds showed a high degree of site fidelity. However, there was some exchange of adults between colonies in Washington and California. Although most Great Lakes'' terns return to the lake where they were born, more than 55% of adult recoveries occurred beyond the natal 10'' X 10'' block in June and July.