The aim of the study was to assess whether increased intra-abdominal pressure affects the clinical course and reflects on the effectiveness of the conservative treatment in patients with severe acute pancreatitis. Data on 37 consecutive patients with severe acute pancreatitis that were collected prospectively included APACHE II score, daily measurement of the intra-abdominal pressure, and clinical routine. Group A consisted of 26 patients with intra-abdominal pressure < 25 cm/H2O during their treatment period, and group B consisted of 11 patients with intraabdominal pressure > or = 25 cm/H2O. SIRS, MODS, complication rate and mortality were analysed. The age, APACHE II scores and hospital stay were similar in both groups. ICU stay was 9.1 +/- 9.6 vs. 20.7 +/- 16.8 days in groups A and B, p < 0.05. SIRS and MODS developed less frequently in group A. More pulmonary complications developed in group B, reaching 64% compared to 19% in group A, p < 0.05. Intra-abdominal pressure had negative interrelation with enterally provided volume (r = -0.45, p < 0.001) and positive interrelation with parenterally provided volume (r = +0.27, p < 0.01) in all. Mortality was zero in group A vs. 36% in group B, p < 0.01. Increase of the intra-abdominal pressure is common during the clinical course of severe acute pancreatitis and can be associated with aggressive fluid replacement therapy. Routine measurement of the intra-abdominal pressure is rational in the clinical setting of the ICU and gives additional criteria for the evaluation of the clinical course and the effectiveness of the treatment. Marked increase of the intra-abdominal pressure should be considered a serious prognostic sign in patients with severe acute pancreatitis.