Pneumocystis carinii pneumonia (PCP) is a well known opportunistic infection in Systemic Lupus Erythematosus (SLE) patients with lymphopenia and treated with corticosteroid or cytotoxics agents. We report a new case of PCP in an untreated SLE with severe lymphopenia. We discuss the origin of lymphopenia in SLE, lymphopenia as a risk factor of Pneumocystis carinii infection, and safety precautions to take.