The introduction of x-ray Computed Tomography (CT) in medicine has effected major improvements in the imaging of soft tissue structures. The same concept can be used with other imaging modalities such as ultrasound with a possible improvement in tissue visualization and characterization. One of the most promising areas for application of the ultrasonic computerized tomographic imaging technique is the detection and diagnosis of lesions in the female breast. The system has been designed and constructed to meet the constraints of breast imaging, but has enough flexibility for general research on ultrasonic CT scanning. The major problem in this application is the mechanical design of the scanner; hence, most of the emphasis in this paper concerns this aspect.