Recent case reports have raised concerns regarding the risks of non-Hodgkin's lymphoma in patients with inflammatory bowel disease treated with immunosuppressive agents. This evidence-based review examines this issue from data derived from the use of immunosuppression in other conditions (and inflammatory bowel disease). We conclude that, in transplant (cardiac and renal) recipients, immunosuppression increases the risk of non-Hodgkin's lymphoma. For non-transplant patients (with psoriasis and rheumatoid arthritis), debate remains as to whether the observed increase in the incidence of non-Hodgkin's lymphoma is due to drug or disease. For inflammatory bowel disease per se, population studies show no significant increase in the risk of non-Hodgkin's lymphoma, with a relative risk of 1.3 (95% confidence interval, 0.9-1.7) compared to expected rates, and several studies of immuno- suppression in inflammatory bowel disease do not appear to confirm a significant rate of lymphoma incidence. Reported cases of lymphoma from single centres should be viewed with caution as evidence of increased risk. If any association exists, it is likely to be of minimal clinical significance compared to the established and more frequent risks of myelosuppression and infection, and is unlikely to outweigh the benefit of immunosuppression in inflammatory bowel disease.