Pneumocystis jirovecii is an atypical fungus exhibiting pulmonary tropism and a highly defined host specificity. It is generally regarded as an opportunistic microorganism causing serious pneumonia in AIDS patients. However, with the currently rising number of patients receiving immunosuppressive therapies for malignancies, allogeneic organ transplantations and autoimmune diseases, Pneumocystis pneumonia is becoming more and more recognized in non-HIV immunosuppressed individuals. The clinical presentation in HIV-infected patients may differ from that in other immunocompromised patients and its diagnosis continues to be challenging as there are no specific symptoms or signs. Cotrimoxazole is the drug of choice for prophylaxis and therapy of any form or severity of Pneumocystis pneumonia, but there are only a few options for other alternative treatments. The management of this pneumonia remains a major challenge for all physicians caring for immunosuppressed patients.