Treatment options are limited in patients with chronic immune thrombocytopenic purpura (ITP) which has been unresponsive to corticosteroids and/or splenectomy. Mycophenolate mophetil (MMF) is effective in many autoimmune disorders including severe and refractory ITP through its targeting of T-cell and B-cell lymphocytes. We report on the efficacy of MMF (1.5-2 g/day) in 16 adults with severe steroid-resistant ITP. MMF was administered for at least 12 weeks (median 37 weeks, range 14-64 weeks). Patients comprised of 10 females and six males, with median pre-treatment platelet counts of 8 × 10(9)/L, median age of 55 years, median ITP duration of 58 months and a median of four prior treatments (range 3-8); nine had been previously splenectomized. Eleven patients (69%) responded after 12 weeks of MMF: 6 (55%) achieving complete remission (CR) and five (45%) achieved partial remission (PR). MMF therapeutic responses were better in those patients who had had fewer prior treatments (p<0.05), and were independent of patient age, sex, disease duration, and splenectomy status (p>0.05). Five of the 11 responders (45%; 3CR/2PR) had sustained remissions; however, six responders (55%; 3CR/3PR) relapsed after median of 14 weeks (range 9-20). Three of the six relapsing patients responded to MMF reinstitution achieving stabile PRs; three were left untreated as none had further bleeding and their platelets remained at "safe" levels (median 30 × 10(9)/L). The MMF treatment was well tolerated; one heavily pretreated patient developed a bronchopneumonia and a second had an episode of diarrhea. MMF used as a second-line agent can produce a sustained response in severe ITP which has been unresponsive to steroid and/or splenectomy without major toxicity.