Twenty-four locality-, age- and sex-matched groups of village residents with no light, moderate and heavy Opisthorchis viverrini infection were examined by ultrasonography. Highly significant differences were observed between the groups in the relative size of the left lobe of the liver and the fasting and post-meal size of the gall-bladder. In addition, indistinct gall-bladder wall, the presence of gall-bladder sludge and strongly enhanced portal vein radicle echoes were most frequently observed in the heavily infected group. Two suspected cases of cholangiocarcinoma were identified from the heavy group. The results highlight the importance of intensity of infection on the frequency and severity of fluke-associated hepatobiliary disease.