Pneumocystis jirovecii (PJ) pneumonia (PJP) is an important opportunistic infection affecting various types of immunocompromised patients and is associated with an increased risk of mortality. PJ is a unique fungal pathogen which is increasingly common and maybe associated with a higher mortality rate in patients without AIDS. We present the characteristics of PJP, diagnosis, and treatment outcomes between AIDS and non-AIDS patients. We conducted a review of studies of AIDS and non-AIDS patients with PJP using PubMed to search for studies until December 2017. The annual incidence of AIDS-PJP decreased from 13.4 to 3.3 per 1000 person-years in industrialized countries, while the incidence of non-AIDS-PJP varied widely. Both groups had similar clinical manifestations and radiological features, but the non-AIDS-PJP group potentially had a more fulminant course, more diffuse ground glass opacities, and fewer cystic lesions. The mortality rate decreased in the AIDS-PJP group after the advent of antiretroviral therapy; however, the mortality rate remained high in both groups. A laboratory diagnosis was usually nonspecific; CD4+ T-cell < 200 cells/mL or < 14% favored AIDS-PJP. Serum 1,3-β-D-glucan (BDG) had a high diagnostic odds ratio. Combining BDG and lactic dehydrogenase improved the diagnosis of AIDS-PJP. Histopathological staining and polymerase chain reactions could not discriminate infection from colonization when the result was positive. The use of antibiotics, prophylaxis, and adjunctive corticosteroids was controversial. Early diagnosis and treatment can be achieved through vigilance, thereby improving the survival rate for PJP in immunocompromised patients.