Pneumonia in critical ill patients, most of them associated with insaturation of an artificial a way and the use of mechanical ventilation, involves important morbi/mortality in the Intensive Care Units. Knowledge of pathogenesis, risk factors, and implicated microorganisms in developing of this major infectious complication, in the context of infections which rise in the critically ill patients, allow us to apply prophylaxis measures which could decrease its incidence, and establish antimicrobial therapy, which permit us to cover all the etiologic possibilities. Availability in the arsenal of the powerful antimicrobial, of a new carbapenemic, meropenem, and based on the different studies and clinic assays, allow to recommend its use with warranties and efficacy, in the empirical or's in concretely those due to Pseudomonas aeruginosa, enterobacteriaceae, (in general or producers of ample spectrum beta-lactamases), and Acinetobacter spp., in monotherapy or combined therapy, with aminoglycosides.