In a retrospective study involving 240 patients with dengue infection, we attempted to identify early predictors of acute liver failure (ALF). Sixteen out of 41 patients with serum AST more than 1000 IU/ml developed ALF compared to none with serum AST less than 1000 IU/ml. Among patients with serum AST more than 1000 IU/ml, presence of two of the three following phenomena, within the first 5 days of illness: elevated serum bilirubin, elevated alkaline phosphatise or persistent nausea and vomiting, predicted development of ALF (93.8% sensitivity, 98.7% specificity, 83.3% positive predictive and 99% negative predictive value). The presence of elevated serum bilirubin, alkaline phosphatase and persistent nausea and vomiting in patients with very high serum AST during the early phase of dengue infection should alert the physician of impending ALF.