The termPneumocystis carinii is now reserved for the animal form of the disease, for humans Pneumocystis jiroveci is appropriated. Incidence of pneumocystis pneumonia (PCP) among patients with systemic rheumatic diseases varies from 0.2% for rheumatoid arthritis to up 12% for Wegener's granulomatosis. Clinical and radiological presentation of pneumocystis pneumonia among non-VIH patients is often difficult to diagnose and the installation can be abrupt. Most of cases of PCP occur during the first 3 months following the beginning of immunosuppressant agents. Mortality during PCP is high with an average of 40% of death, rising 60% in case of mechanical ventilation. Prophylaxis of PCP is needed (without support by randomised studies) for patients with Wegener's granulomatosis, in case of cyclophosphamide or high-dose of methotrexate use except for rheumatoid patients, if a simultaneous treatment by corticosteroids and immunosuppressant agent is required, if a prolonged corticosteroid treatment (> 2 months) is used with dose of prednisone-equivalent > 16mg per day or > 20mg per day > 1month associated with one or more risk factors of PCP among advanced age, denutrition or deep lymphopenia. The best prophylaxis of PCP is cotrimoxazole.