Radio-immunotherapy is a new treatment modality for patients with B-cell non-Hodgkin lymphoma. In radio-immunotherapy, a therapeutic radionuclide is coupled to a monoclonal antibody directed against a tumour-specific or tumour-associated antigen. Biodistribution studies and dosimetry are used in the planning of radio-immunotherapy. Clinical studies, notably in patients with indolent non-Hodgkin lymphoma, have demonstrated the clinical feasibility and efficacy of this treatment. The use of a high dose ofradio-immunotherapy in combination with (high-dose) chemotherapy and peripheral stem-cell transplantation constitutes a supplemental treatment for patients who respond insufficiently or not at all to standard therapy. The exact place of radio-immunotherapy in the treatment of patients with non-Hodgkin lymphomas is not yet clear.