Ibritumomab, an (90)Yttrium ((90)Y) labelled radioimmunoconjugate, is registered in Europe to treat follicular lymphomas. Its mode of action combines the selectivity of monoclonal antibodies with the efficiency of radiotherapy, making it a unique and useful therapeutic agent. This paper is for haemato-oncologists with a decent practice in lymphoma therapy, who have not yet used ibritumomab themselves. It summarizes clinical trials with radioimmunotherapy, indicating clinical situations where it may be specifically useful.