Purpose. To evaluate the accuracy and reliability of two 3-dimensional (3D) ultrasound imaging and measurement techniques in volume measurements using custom-made phantoms. Methods. A total of 20 phantoms with irregular-shaped test objects of known volume (2-9.7 ml) were constructed. The phantoms were scanned using an automated mechanical 3D sonography technique and a free-hand 3D sonography technique. The volumes of the test objects were measured with "parallel planes" and "rotating planes" techniques, respectively. The measured volumes were compared with the actual volumes of the test objects. To evaluate inter- and intraoperator measurement variability, the phantoms were scanned twice by 2 different operators. Results. Both the automated mechanical and the free-hand 3D sonography techniques were accurate and reliabile. Automated mechanical 3D sonography with the parallel planes technique (accuracy, 81.5-83.4%; reproducibility, 91.1%; repeatability, 98.8-99.1%) was slightly more accurate and reliable than the free-hand rotating planes technique (accuracy, 74.7-84.2%; reproducibility, 88.4%; repeatability, 97.3-98%), but the differences were not statistically significant. Conclusion. Both the automated and freehand volume measurement techniques evaluated in this study are accurate and reliable. ; Department of Health Technology and Informatics