Patients with rheumatoid arthritis (RA) are at increased risk of infection compared with the general population. As new DMARDs, in particular biologic agents, become more widely prescribed for the treatment of RA, adverse events that were not previously identified in randomized, controlled trials might develop, including opportunistic and serious infections. Understanding the strengths and weaknesses of data derived from randomized clinical trials, registries and meta-analyses is necessary to interpret the results of these studies. Whereas the risk of infection might be increased for the majority of biologic agents that have been approved for use in RA, differences between these agents might affect patients' susceptibility to specific types of infection, immunocompetence and relative risk of infection.