After years of pre-clinical and clinical testing monoclonal antibodies (mAbs) finally offer new therapeutic choices for patients with haematological and solid malignancies both as unconjugated antibody and as vectors to target radionuclides in radioimmunotherapy (RIT). In recent years some of the most exciting clinical data have come from the use of RIT in the treatment of lymphoma and haematological malignancies and it would now appear highly likely that RIT will play a major role in the treatment strategies for these diseases. For the solid tumours there has also been considerable progress with RIT and mAbs have become a component of treatment protocols for breast cancer. This review highlights the important recent clinical progress that has been made with clinical RIT and provides some new insights into the important mechanisms of action of RIT in haematological malignancies.