Study objective: To investigate the association, between the appropriateness of hospitalization and the course of hospitalization in patients with community-acquired pneumonia (CAP). Methods: We carried out a prospective study of 346 adult patients hospitalized with community-acquired pneumonia (CAP). Appropriateness of hospitalization was assessed with a modified appropriateness evaluation protocol (AEP) based on vital signs and laboratory tests. Hospitalizations that ended in death, lasted more than 4 days, or involved resuscitation, intubation, monitoring, or supplemental oxygen therapy were considered complicated. Results: According to the AEP protocol, hospitalization was not appropriate for 210 of the 346 patients (61%). However, AEP proved to be an insensitive tool for the identification of patients with complicated hospital courses. Half of the 346 patients had complicated courses, including 82 of the 210 patients with inappropriate hospitalization (39%), according to the AEP. Four independent factors, age greater than 50 years, female sex, no antibiotic treatment before hospitalization, and more than 4 days of illness before admission predicted a complicated course in patients with inappropriate hospitalization as determined with the AEP criteria. Conclusion: It is important to avoid the unnecessary hospitalization of patients with CAP. However, this should not be achieved at the expense of unjustified discharge from the emergency department. In the decision to hospitalize, additional prognostic factors, such as those presented here, should be taken into consideration to improve the admission process. This is particularly relevant for cases in in which the AEP is invalid and indications for hospitalization are not clear cut In these patients, a simpler and more precise scoring system should be developed.