Currently, planar arrays providing small elements and good spatial sampling sacrifice sensitivity and an overall aperture extent. Planar arrays with better sensitivity typically use larger elements at the expense of an element directivity (limiting the effective aperture) and degraded spatial sampling. Therefore, volumetric image quality with this technology has yet to rival that provided with 2-D array transducers. Three-dimensional synthetic aperture scanning provides an intermediate solution between the incoherent compounding of 2-D, single-plane images and volumetric imaging with planar arrays. It consists of a mechanical scan of a transducer using a system providing access to the data prior to envelope detection, followed by coherent compounding of the signals acquired at different scan positions to synthetize a larger aperture during the volumetric image reconstruction process. The method has been developed for simple scanning geometries of clinical ultrasound arrays designed for 2-D imaging using translation in the out-of-plane dimension [17], rotation around the median axis of the image [18], and a rocking motion [19]. The method advantageously uses already-developed transducer arrays that are technologically mature and highly sensitive and facilitate the extension of methods to the clinical setting. The time required for mechanical displacements prohibits high-rate scanning of the volume, but the method provides higher image quality than the previously mentioned approaches because coherent compounding can be coupled with a high number of ultrasound signals recorded with very sensitive transducer elements. To date, 3-D synthetic aperture scanning has only been investigated in proof-of-concept studies [17; 18; 19]. It has not yet been developed within a 3-D ultrasound scanner. One reason may be the relatively limited enhancement in spatial resolution that has been obtainedwith the simple scanning geometries that have been investigated thus far. Furthermore, ultrasound platforms that provide access to the raw channel or radiofrequency ultrasound data that are required for synthetic aperture scanning have only recently become widely available. Now is the time to reconsider 3-D synthetic aperture scanning with more advanced scanning geometries for applications that require high image quality but modest volume-scanning rates such as monitoring of a lesion's progression or therapeutic response. In this paper, we investigated the performance of a 3-D, synthetic aperture scanning scheme with a complex scanning geometry based on a rotate-translate scan with a linear ultrasound array. With the combined and predefined motions, a planar surface above the imaged volume was sequentially and efficiently populated with transducers having different spatial positions (array element and translated position) and orientations (angle of rotation about the normal to the surface). This combination of orientations provided a larger synthetic angular aperture in the elevation direction of the array, and thereby improved the resolution and contrast along the elevational axis. The proposed rotate-translate scanning approach was inspired from a scheme previously developed for photoacoustic (PA) tomography [20]. PA tomography is a hybrid imaging modality in which the ultrasound wavefield generated by laser excitation of optical absorbers is captured by transducer elements used only as detectors. The experimental implementation of the scanning scheme in this ultrasonic reception-only configuration resulted in high-quality, 3-D, PA images. In the present study, we demonstrated for the first time the applicability of a rotate-translate scanning scheme for pulse-echo US volumetric imaging and we showed experimentally that higher and more uniform 3-D resolution can be obtained than for existing synthetic aperture approaches. The original scheme proposed for photoacoustic imaging was limited due to the long scan duration.