Abstract Giant armadillos (Priodontes maximus) are one of the most endangered mammals in the Gran Chaco. They are largely nocturnal, highly fossorial and solitary, characteristics that have limited the understanding of their behavior and ecology. We report on the results of a study of the structure of 32 giant armadillo burrows in 25,000 ha of semi-arid forest owned by Toba aborigines of Formosa, Argentina. Burrow entrances were on average 43 cm wide and 36 cm high and more likely to be facing west (24) than east (8).