Microaspiration of contaminated oropharyngeal secretions and gastric contents frequently occurs in intubated critically ill patients, and plays a major role in the pathogenesis of ventilator-associated pneumonia. Risk factors for microaspiration include impossible closure of vocal cords, longitudinal folds in high-volume low-pressure polyvinyl chloride cuffs, and underinflation of tracheal cuff. Zero positive end expiratory pressure, low peak inspiratory pressure, tracheal suctioning, nasogastric tube and enteral nutrition increase the risk for microaspiration. Other patient related factors include supine position, coma, sedation, and hyperglycemia. Technetium 99 labelled enteral feeding is probably the most accurate marker of microaspiration in critically ill patients. However, use of this radioactive marker is restricted to nuclear medicine departments. Blue methylene is a reliable qualitative marker of microaspiration. However, fiberoptic bronchoscopy is required to diagnose microaspiration of blue dye in ICU patients. Quantitative pepsin measurement in tracheal aspirates is accurate in diagnosing microaspiration of gastric contents in critically ill patients. In addition, this marker is easy to use in routine practice. However, pepsin should be detected rapidly after aspiration. In vitro, and clinical studies suggested that semirecumbent position, polyurethane cuffs, positive end expiratory pressure, low-volume low-pressure cuff, and continuous control of cuff pressure were efficient in reducing microaspiration in ICU patients. Other preventive measures such as subglottic aspiration, tapered shape cuff, guayule latex cuff, lateral horizontal patient position, gastrostomy tube, and postpyloric feeding require further investingation.