An ultrasonic diagnostic imaging system is provided with a scanning guide which assists a user in conducting three dimensional ultrasonic scanning of a patient. The guide is visual or audible or both, and gives the physician a real time indicator by which to gauge the rate and duration of three dimensional ultrasonic scanning. In a constructed embodiment the scanning guide is modulated by a counter coupled to cine memory, in which image frames are stored for three dimensional processing. As the cine memory fills toward capacity with ultrasonic image frames, the scanning guide is modulated in correspondence with the filling of the memory. A visual indicator (100) of the ultrasonic frame sequence in memory is also provided, on which the user can move markers to eliminate frames at the beginning or end of the sequence from the three dimensional reconstruction.