Several monoclonal antibodies are now approved for cancer therapy, such as rituximab, an anti-CD20 monoclonal antibody for the treatment of B-cell non-Hodgkin's lymphoma. Such 'naked' antibodies can recruit the body's immune effector mechanisms to kill cells expressing the target of the antibody. In recent years, the linking of radionuclides to antibodies to either augment inherent activity or to exploit the specific targeting properties of monoclonal antibodies has been a major area of development. Two radionuclide-bearing monoclonal antibody therapies have recently been approved by the US FDA, and several more are in clinical trials. Here, we discuss the development and use of radiolabelled monoclonal antibody therapies, with a focus on radiolabelled monoclonal antibodies that have been evaluated in clinical trials.