Community-acquired pneumonia (CAP) has a high incidence and involves an important consumption of healthcare resources. The present authors analysed the influence of comorbidity, initial severity and complications upon the direct costs associated with hospitalised CAP patients.Direct hospitalisation costs (room cost, treatment, laboratory and diagnostic tests) were assessed in a prospective, observational study of 271 patients admitted to a hospital ward due to CAP.The mean¡SD patient age was 70¡15 yrs. The mortality rate was 11.1%. Complications were found in 72.3% and comorbidities in 74.9%. The median (interquartile range) total cost was J1,683 (J1,291-2,471) and the component costs were: room cost J1,286 (J857-1,714); laboratory tests J212 (J171-272); treatment J187 (J114-304); and diagnostic procedures J58 (J29-122). Complications and higher Pneumonia Severity Index increased the costs, but age and comorbidity did not. A logistic regression analysis to predict high cost (.J1,683) showed that infectious (odds ratio 6.8, 95% confidence interval 1.3-36), digestive (5.9 (1.5-22.8)), pulmonary (2.6 (1.4-4.7)) and other complications (3.9 (1.8-8.4)) were independent risk factors, as were previous hospitalisation (2.3 (1.2-4.3)) and hypoalbuminaemia (2 (1.1-3.6)).Complications, hypoalbuminaemia and previous hospitalisation were the main determinants of high direct costs of hospitalisation due to community-acquired pneumonia. Neither age nor comorbidities were independently associated with cost.