The usefulness of a new three-dimensional ultrasound (3DUS) volumetric system developed recently was validated in volume measurement of liver tumor in the present study. The system was used to estimate the volumes of 22 regular phantoms, 25 irregular phantoms and 37 liver tumors from 33 patients. The results showed that the consumed time of measurement with the system ranged from 1 to 15 min, depending on different rotation angles. The measured volumes at different rotation angles all significantly correlated with the true volumes and there were no significant differences among measured volumes at different angles. The measurement error of 3DUS was 0.3% +/- 3.3% in regular phantoms, -0.4% +/- 3.7% in irregular phantoms and 0.9% +/- 11.3% in liver tumors, respectively, as compared with -5.3 +/- 9.4%, 13.6 +/- 28.0% and 15.3 +/- 37.3% for two-dimensional ultrasound, respectively (all p < 0.05). The volume estimation with 3DUS also had significant intraobserver and interobserver reproducibility both in vitro and in vivo. It can be concluded that the new system that we used can greatly reduce the consumed time and manual labor for volume measurement with high accuracy and reproducibility. 3DUS volumetry using the new system is more acceptable and valuable in clinical practice and is expected to be useful for evaluation of the efficacy of tumor therapy in situ in patients with hepatic tumors.