Prostate cancer is dependent on the action of steroid hormones on the receptors. Endocrine therapy inhibits hormone production or blocks the receptors, thus providing clinical benefit to many, but not all, oncological patients. It is difficult to predict which patient will benefit from endocrine therapy and which will not. Positron emission tomography (PET) imaging of androgen receptors (ARs) may provide functional information on the likelihood of endocrine therapy response in individual patients. In this chapter, the utility of [18F]FDHT-PET imaging in prostate cancer expressing AR is reviewed. The role of [18F]FDHT-PET as prognostic biomarker and its role in the development of new endocrine therapies are discussed as well.