Within the past five years, 3D ultrasonography has developed to the degree that it offers both the patient and the examiner an entirely new visual experience in prenatal diagnosis. With the system described here (Kretz-technik, Austria), any desired plane can be displayed within the stored volume, and within seconds a high-quality 3D surface or transparent image can be calculated and displayed on the ultrasound monitor without need for an external workstation. All of this can be performed routinely in the clinical setting. 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 2D ultrasound scans with a 3D examination using an abdominal volume transducer. A comparison of the 2D and 3D techniques shows that 3D provides a diagnostic gain in a large percentage of cases (64.2%). The simplest 3D 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 3D display (orthogonal format plus a 3D surface or transparent view) provided a diagnostic gain in 71.5% (233/326) of the cases. This higher percentage resulted from the additional 3D surface reconstruction, the ability to view and evaluate the fetus from various angles, the ability to determine the exact size of a fetal defect, the depiction of skeletal anatomy in the transparent mode, and the improved delineation of complex malformations. Problems with 3D imaging are encountered in patients with pronounced oligohydramnios, which prevents surface reconstruction, and in the examination of moving objects, which produce motion artifacts.