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The population size, breeding, and annual cycle of Antarctic terns (Sterna vittata bethunei) at the subantarctic Snares Islands were studied intermittently from 1976 to 2002. During the 1983/84 and 1984/85 breeding seasons the population comprised a minimum of 65 breeding pairs. Laying dates extended from mid Sep to late Mar, with peak laying in late Oct-early Nov. Clutch size averaged 1.33 (range 1-2 eggs) and did not change through the breeding season. Both parents incubated. Hatching success was 92.7% and both parents fed the young. Fledging success was 75%, and so overall breeding success was 69.6%. Chicks were fed mostly fish by both parents and 1-chick broods were fed smaller fish and less frequently than 2-chick broods. The youngest bird recorded breeding was at least 3 years old. After the breeding season (from Mar), the terns formed flocks and moulted in the vicinity of the Snares Islands. Following the completion of moult (from Apr) they tended to move offshore, only returning to the shelter of the islands during severe weather. From mid Jul, the terns tended to roost in flocks at the Snares Islands before dispersing to form pairs and defend nesting sites.