To determine the effect of selective internal radiation therapy (SIRT) and hepatic arterial chemotherapy (HAC) on normal liver volume and spleen volume in patients receiving these treatments for advanced liver cancer. In a phase III clinical trial to assess the benefit of SIRT over HAC one group of patients received SIRT + HAC while a second group received HAC only. All patients in this trial who had abdominal CT scans available before treatment, and at 3, 6, and 12 months after treatment were evaluated. Changes in normal hepatic parenchyma (NHP) volume, portal vein diameter and spleen volume were calculated for each patient and analysed for significant trends. The mean NHP volume decreased by 17% (P = 0.001) 12 months after treatment among patients receiving SIRT + HAC (N = 22), while the mean NHP volume among patients treated with HAC only (N = 15) was unchanged at 12 months. The mean portal vein diameter increased by 9% in both treatment groups, P = 0.048 and P < 0.001, respectively. The mean spleen volume increased by 48% (P < 0.001) and 26% (P = 0.001), respectively, in the two groups 12 months after treatment started. There was no clinical evidence of hepatic failure, portal hypertension or splenic dysfunction in any of the patients. Treatment of patients with SIRT + HAC causes contraction of the normal hepatic parenchyma, while treatment with HAC alone has no significant effect. Treatment with either SIRT + HAC or HAC alone causes a significant increase in portal vein diameter and spleen volume by 12 months after treatment. The increase in spleen volume and portal vein size is likely to be due to portal hypertension resulting from scarring within the liver as a result of chemical and radiation hepatitis. Copyright 2001 Wiley-Liss, Inc.