Radionuclide-based theranostic strategy has been widely used in diagnosis and treatment of patients with hyperthyroidism or differentiated thyroid cancer for a long time, and sodium iodide symporter gene is the radionuclide-based reporter gene used in theranostics. Theranostics, which is a promising approach, offering the ideal combination of accurate diagnosis and successful therapy in various clinical fields, is expected to become a key area of personalized medicine. Rapid advancements in biotechnologies using theranostic reporter genes and theranostic radiochemistry have led to development of the concept of theranostics using radionuclide-based imaging reporter genes; the theranostic approach is almost ready for application in a limited arena of clinics. In order to fulfill both the diagnostic and therapeutic purposes, theranostics with radionuclide-based imaging reporter requires use of successful combinations of various components, such as radionuclide-based reporter genes, promoters/enhancers that regulate expression of reporter genes, delivery vectors/vehicles, imaging or therapeutic probes and prodrugs, transductional and transcriptional targeting strategies, transgene amplification systems, etc. In this review, overview and recent updates on theranostics using radionuclide-based imaging reporter genes will be discussed.