Pneumonia Severity Index (PSI) score is a score developed to estimates the mortality for adult patients with community acquired pneumonia. It will takes account many factors including demographic factors, comorbid illness, physical examination findings, laboratory, and radiographic findings. The patient will then be classified into five class risk-categories. Higher points will lead to higher risk-categories and also higher mortality rate from the community acquired pneumonia.

The pneumonia severity index (PSI) score is also can be used to help medical practitioner to decide whether outpatient or hospitalization is recommended for patients with community acquired pneumonia. Patients with class risk III-V will benefit for hospitalization and observation due to higher mortality rate. However clinical judgement of the medical practitioner and local policy must also be taken account.