PURPOSE: To correlate CT features with peripheral eosinophilia in patients with idiopathic hypereosinophilic syndrome involving the liver. MATERIALS AND METHODS: During the last three years, features of liver involvement in nine of 20 patients with idiopathic hypereosinophilic syndrome were evaluated on CT. The shape and distribution of intrahepatic low densities and the presence of hepatomegaly and/or splenomegaly were reviewed on CT, and the percentage of eosinophils in peripheral blood was also determined. In seven cases, interval change in hepatic lesion and the percentage of eosinophils were reviewed on follow-up examination. RESULTS: On initial CT, varying low-density patterns were seen in the liver in all cases ; hepatomegaly was seen in four cases, and hepatosplenomegaly in two. The percentage of eosinophils was 89% in a case with diffuse patch low densities in the liver, 65-85% in three cases with numerous nodular low density lesions, 12-29% in four cases with multiple (below ten) nodular or small geographic hypodense lesions, and 24% in a case with a single nodular hypodense lesion. On follow-up CT, seven patients showed a decrease in the percentage of eosinophils, and in six, improved intrahepatic low densities were seen. CONCLUSION: On CT, intrahepatic low densities were seen in patients with idiopathic hypereosinophilic syndrome, and these were distributed more extensively when peripheral eosinophilia was more severe. With improvement in peripheral eosinophilia, the low densities also improved.