Rationale: To identify pathogens that require different treatments in community-acquired pneumonia (CAP), we propose an acronym, "PES" (Pseudomonas aeruginosa, Enterobacteriaceae extendedspectrum β-lactamase-positive, and methicillin-resistant Staphylococcus aureus). Objectives: To compare the clinical characteristics and outcomes between patientswithCAP caused by PES versus other pathogens, and to identify the risk factors associated with infection caused by PES. Methods: We conducted anobservational prospective study evaluating onlyimmunocompetentpatientswithCAPand anestablished etiological diagnosis. We included patients from nursing homes. We computed a score to identify patients at risk of PES pathogens. Measurement and Main Results: Of the 4,549 patients evaluated, we analyzed 1,597 who presented an etiological diagnosis. Pneumonia caused by PES was identified in 94 (6%) patients, with 108 PES pathogens isolated (n = 72 P. aeruginosa, n = 15 Enterobacteriaceae extended-spectrum b-lactamase positive, and n = 21 methicillin-resistant Staphylococcus aureus). These patients were older (P = 0.001), had received prior antibiotic treatment more frequently (P<0.001), and frequently presented with acute renal failure (P = 0.004). PES pathogens were independently associated with increased risk of 30-day mortality (adjusted odds ratio = 2.51; 95% confidence interval = 1.20-5.25; P = 0.015). The area under the curve for the score we computed was 0.759 (95% confidence interval, 0.713-0.806; P<0.001). Conclusions: PES pathogens are responsible for a small proportion of CAP, resulting in high mortality. These pathogens require a different antibiotic treatment, and identification of specific risk factors could help to identify these microbial etiologies.