During the Second World War, both Chile and Argentina advanced sovereignty claims to the Antarctic Peninsula and surrounding sub-Antarctic islands that overlapped substantially with claims that the United Kingdom had made in 1908 and 1917. This article explores the emergence of the concept of a South American Antarctica during this period. Although, at one level, the two South American countries attempted to create a united front against the British, they actually decided to press their claims to Antarctica for different and sometimes conflicting reasons. In Argentina, nationalists connected the question of sovereignty in Antarctica with their claims to the Malvinas and with a broader struggle against a supposed British economic imperialism. In Chile, patriotic officials were less concerned with British claims to the Antarctic Peninsula and more worried about Argentina's growing interest in the region. The article concludes that a better understanding of the complex and contradictory history of the emergence of the idea of South American Antarctica during the Second World War leads to an enhanced appreciation of the subsequent development of the so-called ‘Antarctic Problem’ as it developed over the next 15 years. In order to avoid the artificiality of the term ‘Falklands (Malvinas)’, the British terms ‘Falklands’ and ‘Falkland Islands’ have been used when discussing the United Kingdom's position, and the Argentine term ‘Malvinas’ when discussing that of Argentina.