In HIV-negative adults, Pneumocystis jirovecii pneumonia can be observed when immunodeficiency is present, especially in case of drug-induced immune suppression (steroids, chemotherapy, transplantation). Clinical, radiological, and biological presentations are different in HIV-positive and HIV-negative individuals with different immunodeficiency profiles. In HIV-negative patients, dyspnea occurs more quickly (median duration of 5 days to get a diagnosis), diagnosis is more difficult because of less Pneumocystis in bronchoalveolar lavage, and mortality is higher than in HIV-positive individuals. Lung CT-scan typically shows diffuse ground glass opacities, but peri-bronchovascular condensations or ground glass opacities clearly limited by interlobular septa can also be observed. Lymphopenia is common but CD4+ T-cells count is rarely performed. HIV-negative patients with Pneumocystis pneumonia are co-infected with bacteria, viruses or fungi in about 30% cases. Bronchoalveolar lavage is often more neutrophilic than in HIV-positive individuals. PCR and β-D-glucan have good sensitivity but poor specificity to diagnose Pneumocystis pneumonia. Trimethoprim-sulfamethoxazole remains the first choice of treatment. Duration is 14 days in HIV-negative patients whereas it is typically of 21 days in HIV-positive individuals. Adjunctive corticosteroids are of beneficial effect in HIV-positive adult patients with substantial hypoxaemia but are not recommended in HIV-negative patients, as they could be deleterious in some individuals.