AIM: To determine whether the hematocrit (Hct) at admission or at 24 h after admission was associated with severe acute pancreatitis (AP), organ failure (OF), and pancreatic necrosis.METHODS: A total of 336 consecutive patients with a first AP episode were studied. Etiology, Hct values at admission and at 24 h, development of severe AP according to Atlantas criteria, pancreatic necrosis, OF and mortality were recorded. Hemoconcentration was defined as Hct level ＞44% for males and ＞40% for females. The t-test and χ2 test were used to assess the association of hemoconcentration to the severity, necrosis and OF.Diagnostic accuracy was also determined.RESULTS: Biliary disease was the most frequent etiology(n = 148). Mean Hct levels at admission were 41±6%for females and 46±7% for males (P＜0.01). Seventyeight (23%) patients had severe AP, and OF developed in 45 (13%) patients. According to contrast-enhanced computed tomography scan, 36% (54/150) patients showed pancreatic necrosis. Hct levels were elevated in58% (55/96) and 61% (33/54) patients with interstitial and necrotizing pancreatitis, respectively. Neither Hct levels at admission nor hemoconcentration at 24 h were associated with the severity, necrosis or OF. Sensitivity,specificity and positive predictive values for both determinations were very low; and negative predictive values were between 61% and 86%, being the highest value for OF.CONCLUSION: Hct is not a useful marker to predict a worse outcome in acute pancreatitis. In spite of the high negative predictive value of hemoconcentration, the prognosis gain is limited due to an already high incidence of mild disease.