Hepatosplenic T cell lymphoma (HSTCL) are rare cancers ( approximately 100 published cases worldwide) and comprise 5% of peripheral T cell lymphomas. As of October 5, 2006, the FDA's Adverse Event Reporting System has received 8 cases of HSTCL in young patients using infliximab, a tumor necrosis factor-alpha blocking agent, to treat inflammatory bowel disease (6 of the 8 cases had a fatal outcome). All 8 patients were receiving concomitant immunosuppressant therapy (eg, azathioprine, prednisone). It has not been established that infliximab had an exclusive or primary role in the pathogenesis of these HSTCL cases; however, it appears that patients using this product may be at greater risk for developing this rare lymphoma.