The RATIO registry is a French registry designed by a multidisciplinary group to collect data on opportunistic and severe bacterial infections and lymphoma in patients treated with TNF-a antagonists ( infliximab, etanercept and adalimumab). A total of 486 medical units in metropolitan France participate in the RATIO registry. All diagnosis are retained after validation by 2 qualified infectious disease or haematologist physicians (on the basis of the standardized case report form, the hospitalisation summary, and the microbiological and radiological results). Risk factors for developing these conditions when treated by TNF-a antagonists will be identified in a case control study. Incidence of these diseases will be calculated.