Compare hemoconcetration, APACHE II and Ranson scores as early predictors of severity defined by Atlanta criteria in patients with acute pancreatitis at Hospital Nacional Cayetano Heredia. Retrospective descriptive study between December 2009 to November 2010 done using a data collection sheet to gather study relevant information. We classified acute pancreatitis into mild or severe according to Atlanta symposium criteria for organ failure and/or local complications. Comparison of hematocrit values was made using a t Student test to detect a significant difference and the area below the ROC curve was analyzed. Counting with 151 patients, 103 women (68.2%), with mean age of 45.5 ± 19.17 years, 112 mild pancreatitis (74.2%) and 39 severe (25.8%). Mean hematocrit in mild cases was 38.40 ± 4.77% and 39.78 ± 7.35% in severe group with p equal to 0.182. Area below the ROC curve of 0.89 y 0.68 for APACHE II and Ranson scores respectively. Hemoconcentration and Ranson proved not to be as useful as APACHE II score in predicting severity in acute pancreatitis.