This invention discloses a system and method for providing Doppler flow velocity data that is corrected for misalignment between the flow direction within a vessel and the beam orientation of the ultrasound probe. A conventional ultrasonic Doppler color mapping system was adapted to include an apparatus to measure and record the free space position and orientation of the ultrasonic probe. A set of 2D image planes, which need not be parallel, is acquired. A structural representation derived from the acquired data is used to determine the flow direction for the imaged vessel. This apparatus and method has advantages over other systems because it offers the ability to measure flow distributions with a hand-manipulated probe.