Clinical evolution in patients affected by community acquired pneumonia varies from a mild and low risk infectious disease to an extremely severe, life threatening disease. Commonly, immunocompetent adults without co-morbidities or severe risk factors cared for at out patient clinic have low risk of complications and death (mortality below 1-2%); it increases to 5-15% in patients with co-morbidities and/or with specific risk factors that are admitted into the hospital and reaches 20-50% in those patients admitted into ICUs. Evaluation of severity in patients with pneumonia allows the prediction of disease evolution, establishing the proper setting of care, the type-of microbiological tests needed, and to choose the best empiric antibiotic treatment. It is suggested that patients be in three risk categories: low risk (mortality under 1-2%) susceptible to ambulatory treatment; high risk patients (mortality 20-30%) that need specialized wards; and intermediate risk patients, with co-morbidities and/or risk factors for complicated clinical evolution and death, but cannot be classified in a specific category. In the ambulatory setting, without availability of complete laboratory exams, it is recommended to evaluating the severity of pneumonia considering the following clinical variables: age over 65 years, presence of co-morbidities, sensorial compromise, vital signs alteration, degree of radiological involvement: multilobar, bilateral findings, cavitations), pleural effusion and arterial oximetry < 90%. However, clinical judgement and the physician´s experience must predominate over predictive models, which are not infallible.Key words: pneumonia, prognosis, severity of illness index. Palabras clave: neumonía, pronóstico, evaluación de gravedad del paciente. Evaluación de la gravedad en la neumonía adquirida en la comunidad El cuadro clínico del paciente con neumonía adquirida en la comunidad (NAC) que solicita atención en el medio ambulatorio (consultorios y servicios de urgencia) puede variar entre un cuadro infeccioso leve de bajo riesgo de complicaciones hasta uno de extrema gravedad con riesgo vital 1-3 [Ib] suggestedtreavteiesg36cióerveo de ervex2 Tw d that