The crystal structure of a mutant androgen receptor (AR) ligand-binding domain (LBD) in complex with the agonist 9α-fluorocortisol has been determined at 1.95 Å resolution. This mutant AR contains two mutations (L701H and T877A) and was previously reported as a high-affinity cortisol/cortisone responsive AR (AR^ccr) isolated from the androgen-independent human prostate cancer cell lines MDA PCa 2a and 2b (Zhao et al. Nature Med. 2000, 6, 703−6). The three-dimensional structure of the AR^ccr LBD complexed with 9α-fluorocortisol shows the typical conformation of an agonist-bound nuclear receptor in which helix 12 is precisely positioned as a “lid” for the ligand-binding pocket. Binding of 9α-fluorocortisol to the AR^ccr involves favorable hydrogen bond patterns on the C17 and C21 substituents of the ligand due to the mutations at 701 and 877 in the AR^ccr. Our studies provide the first structural explanation for the glucocorticoid activation of AR^ccr, which is important for the development of new therapeutic treatments for androgen-independent prostate cancer.