We aimed to develop criteria of hepatomegaly on erect plain radiography by comparing the results with those of ultrasonography. Right-sided longitudinal length and second lumbar vertebra ratio, of 22 cm and 6, respectively, detected hepatomegaly with over 90% accuracy, with higher success rates for the lumbar vertebral ratio. Corresponding values for normal size were 20 cm and 5. Sonography revealed high correlation with these results. We concluded that liver size measured on erect plain radiography was larger than but similar to that measured by sonography, and that right-sided longitudinal length and the lumbar vertebral. ratio are reliable criteria showing good correlation with the results of sonography.