For more than 5 years, infliximab and etanercept have been utilized to treat rheumatoid arthritis and Crohn's disease. There is therefore much post-approval data on their side effects. A variety of Medline searches were done at the beginning of June 2004 using the terms 'etanercept', 'infliximab' and 'adalimumab' and the words 'lymphoma', 'infection', 'congestive heart failure', 'demyelinating disease', 'lupus', 'antibodies', 'injection site reaction', 'systemic', 'side effects' and 'skin'. Approximately 150 articles were so identified. In addition, FDA and manufacturers' data obtained by internet searches using Google were reviewed. The important side effects that have been most extensively related to TNFalpha blockers include: lymphoma, infections, congestive heart failure, demyelinating disease, a lupus-like syndrome, induction of auto-antibodies, injection site reactions, and systemic side effects. The risk of these side effects is very low. Nevertheless, it is important for clinicians to be aware of these side effects when prescribing therapy.