The recent developments of nuclear medicine in oncology have involved numerous investigations of novel specific tumor-targeting radiopharmaceuticals as a major area of interest for both cancer imaging and therapy. The current progress in pharmaceutical nanotechnology field has been exploited in the design of tumor-targeting nanoscale and microscale carriers being able to deliver radionuclides in a selective manner to improve the outcome of cancer diagnosis and treatment. These carriers include chiefly, among others, liposomes, microparticles, nanoparticles, micelles, dendrimers and hydrogels. Furthermore, combining the more recent nuclear imaging multimodalities which provide high sensitivity and anatomical resolution such as PET/CT (positron emission tomography/computed tomography) and SPECT/CT (combined single photon emission computed tomography/computed tomography system) with the use of these specific tumor-targeting carriers constitutes a promising rally which will, hopefully in the near future, allow for earlier tumor detection, better treatment planning and more powerful therapy. In this review, we highlight the use, limitations, advantages and possible improvements of different nano- and microcarriers as potential vehicles for radionuclides delivery in cancer nuclear imaging and radiotherapy.