Radionuclide therapy is a type of targeted therapy that can be useful in the treatment of several malignant tumors. Compared with other forms of systemic therapy used in cancer - including chemotherapy - it has the advantage of sparing biological structures adjacent to the tumor cells. This treatment modality has registered significant advances since its first use for the treatment of tuberculous skin lesions in the 1900s. This paper reviews the characteristics and clinical applications of therapeutic radionuclides commonly used in the oncology clinical practice, and discusses future potential applications.