Recent assessments of Earth's dwindling wilderness have emphasized that Antarctica is a crucial wilderness in need of protection(1,2). Yet human impacts on the continent are widespread(3-5), the extent of its wilderness unquantified(2) and the importance thereof for biodiversity conservation unknown. Here we assemble a comprehensive record of human activity (approximately 2.7 million records, spanning 200 years) and use it to quantify the extent of Antarctica's wilderness and its representation of biodiversity. We show that 99.6% of the continent's area can still be considered wilderness, but this area captures few biodiversity features. Pristine areas, free from human interference, cover a much smaller area (less than 32% of Antarctica) and are declining as human activity escalates(6). Urgent expansion of Antarctica's network of specially protected areas(7) can both reverse this trend and secure the continent's biodiversity(8-10).