Cu-64 is an isotope of copper with potential use in PET imaging and the targeted radiotherapy of cancer. It has a complex decay scheme, with electron capture, beta-emission and positron emission branches. Cu-64 in the most simple salt form as well as linked to a variety of bioactive molecules can be used as theranostic agents in human malignancies such as prostate, glioblastoma, melanoma, breast cancers) and also diagnosis of human copper-associated diseases such as atherosclerosis, Alzheimer’s etc. There are some examples of investigational Cu-64-based radiopharmaceuticals: Cu-64-ATSM for imaging hypoxia, Cu-64-labeled peptides for tumor-receptor targeting, Cu-64-labeled monoclonal antibodies for targeting tumor antigens, and Cu-64-labeled nanoparticles for cancer targeting.