Infections are a major cause of morbidity and mortality in patients with connective tissue diseases. Infectious consequences are caused by systemic disorders by themselves and the immunosuppressive treatments. Systemic lupus erythematosus and Wegener's granulomatosis are associated with the higher risk of infection. Primary prophylaxis of Pneumocystis carinii pneumonia has to be systematically given in patients with Wegener's granulomatosis and in other patients with connective tissue diseases if their CD4-cell count is lower than 200/mm3. Intensitification of immunosuppression during the course of systemic disorders can not be performed before any infection has been eliminated.