Changes of portal venous hemodynamics were investigated in 32 patients with cystic fibrosis (CF) with a mean age of 11.6 years. Hepatic profile of these patients included total bilirubin and albumin together with determination of size and echogenicity of the liver and spleen, determination of the diameter of the portal vein by real-time sonography and quantitation of flow volume of the portal vein using Duplex Doppler sonography. As a control, 35 age matched healthy children were also examined. Diameter of the portal vein was significantly increased in CF patients versus controls. Comparison of the mean flow volume of the portal vein showed a significant increase in CF-patients over 12 y old versus controls. In patients less than 12 y no significant difference of flow volume of the portal vein between CF-patients and controls was noted. The increase of diameter and flow volume of the portal vein suggest an adaptive mechanism in the pressure-volume relationship of the portal venous system in patients with CF.