Nanotechnology is a novel but rapidly advancing domain of Therapeutics. Nanoscale-diameter particles such as liposomes and dendrimers may be conscribed for the effective and safe administration of several drugs. The main advantages of nanosystem-mediated drug delivery are the following; i) sufficient absorption, ii) delayed metabolism and excretion, iii) longer half-life, iv) ability to cross several anatomical barriers, v) enhanced accumulation in specific target-tissues (e.g. malignant tumors), vi) lower toxicity of the drug. During the last years there is a growing interest around the potential contribution of Nanotechnology in the development of Nuclear Medicine and vice versa. Radioactive agents called radiopharmaceuticals are already used in several medical procedures. Exploiting their ability to accumulate selectively on specific organ-targets, radiopharmaceuticals serve in diagnostic applications, such as scintiscan, PET scan and in therapy of several diseases (e.g. thyroid cancer). The use of nanosystems may further ameliorate the properties of radiopharmaceuticals regarding their targeting ability and their unique pharmacokinetic properties. On the other hand radionuclides may serve in experimental studies for the pharmacological evaluation of nanosystems. Nevertheless further research is required in order to confirm the effectiveness and safety of nanosystem-mediated radiopharmaceutical applications.