The physical principles and clinical applications of a high-resolution, dynamically focused phased-array real time ultrasound are described. Advantages of the real time technique include rapid survey capability, efficient selection of an appropriate tomographic plane, identification of pulsating structures, and dynamic studies. The capabilities of a high resolution phased array with extended dynamic focusing to a range of 15-20 cm are demonstrated in vascular, abdominal, and obstetric imaging. Appropriate clinical examples showing normal and pathological anatomy are presented. Comparisons with conventional B scans are illustrated.