The reproductive ecology of the Least Tern (Sterna antillarum) was examined at four nesting colonies along the Lower Mississippi River during the 1995-1997 breeding seasons. Nest success, hatching success, and reproductive success were calculated in order to estimate productivity and evaluate reproductive status. Nesting colonies varied in size from 172 to 550 nests, with average clutch sizes ranging from 1.9-2.7 eggs/nest. Both nest success, the proportion of nests from which at minimum one egg hatched, and hatching success, the proportion of eggs that hatched, were significantly higher in 1995 (97% and 94% respectively) as compared to 1996 and 1997 (∼40%). Reproductive success averaged between 0.28-1.27 fledglings/clutch. Predation and untimely flooding were the largest negative impacts upon successful tern reproduction.