Summary. Radioimmunotherapy is a new antineoplastic treatment modality combining the effects of irradiation and monoclonal antibodies. 90Y-ibritumomab tiuxetan is a monoclonal antibody directed against the CD20 antigen to which a radioactive isotope of yttrium is attached, used for treating follicular lymphomas (FL). Using this compound we treated 8 patients with FL relapsing or refractory to combinations of rituximab and chemotherapy. Severe neutropenia developed in 5, and severe thrombocytopenia and anemia in 3 patients. Serious infections developed in 2 patients, one died. Six patients responded to treatment, 4 are still in remission after a median follow-up of 15 months, 2 died of lymphoma. Best response was achieved in low-risk patients with a low tumor burden. 90Y-ibritumomab tiuxetan is an effective treatment for FL with significant hematological toxicity and a high price.