OBJECTIVE Within the past several years, 3-D ultrasonography has developed to a highly advanced diagnostic procedure. The aim of this study was to define the advantages of 3-D ultrasound in prenatal diagnosis in comparison to the conventional 2-D technique. METHODS Since 1989 we have routinely examined a total of 458 fetuses (242 normal and 216 with anomalies) between 16 and 38 weeks of gestation, supplementing our conventional 2-D ultrasound scans with a 3-D examination using an abdominal volume transducer (Combison 330 and 530, 3.5/5 MHz, Kretztechnik Austria). With this system all 3 orthogonal planes can be displayed on the ultrasound monitor and high-quality 3-D surface or transparent images can be calculated and displayed on the ultrasound monitor as well without need for an external workstation. RESULTS The comparison of the 2-D and 3-D techniques shows that 3-D provides a diagnostic gain in a large percentage of cases (64.2%). The simplest 3-D technique of the orthogonal image display provided a diagnostic gain in 46.2% (61/132) of the cases owing to the accurate topographic depiction of the desired image plane. The combined 3-D display (orthogonal format plus a 3-D surface or transparent view) provided a diagnostic gain in 71.5% (233/326) of the cases, due to the additional 3-D surface reconstruction and the ability to depict the skeletal anatomy in the transparent mode. Problems with 3-D imaging are encountered in patients with oligohydramnios, which prevents surface reconstruction, and in the examination of moving objects, which produce motion artifacts. CONCLUSIONS Today 3-D ultrasonography offers both the patient and the examiner an entirely new visual experience in prenatal diagnosis.