BACKGROUND There has been a dramatic increase in the use of intensive care units (ICUs) over the past 25 years. Greater use of validated measures of illness severity may better inform ICU admission decisions in patients with community-acquired pneumonia. This article examined predictors of ICU admission and hospitalization costs, including the pneumonia severity index (PSI) and CURB-65 (confusion, uremia, respiratory rate, blood pressure, age ≥65 years) scores. METHODS The study identified 422 patients hospitalized for community-acquired pneumonia, ascertaining patient characteristics by chart review and extraction of administrative data. Multivariate logistic regression was performed to quantify the association of the PSI, CURB-65 and comorbidities with ICU admission. The predictors of cost were estimated using a generalized linear model. RESULTS Compared to 194 general medicine patients, certain clinical and radiographic findings were more common among 228 ICU patients. Compared to PSI reference group I/II/III, ICU admission was strongly associated with risk class IV (odds ratio [OR], 3.06; 95% confidence interval [CI], 1.63-5.72) and V (OR, 4.84; CI, 2.44-9.62), and also CURB-65 ≥3 (OR, 2.90; CI, 1.51-5.56). The relative increase in mortality among PSI risk class V (compared to IV) patients was 2.68 times higher in general medicine, compared with the ICU. Among ICU admissions, risk class V was associated with an additional cost of $14,548 (95% CI, $4,232 to $24,864). CONCLUSIONS Illness severity and chronic pulmonary disease are strong predictors of ICU admission. More extensive use of the PSI may optimize site-of-care decisions, thereby minimizing mortality and unnecessary resource utilization.