A volumetric method for 2-D flow imaging is provided in medical diagnostic ultrasound. Flow data for a volume is acquired. For more rapid acquisition, broad beam transmission and reception along many scan lines distributed in the volume is used. The volumetric flow data is filtered, such as by calculating statistical information, to generate a planar/2-D flow image. The statistical information from the three-dimensional flow data is used to determine the display values for the flow imaging.