In 3D ultrasound systems that form a 3D image by tracking the ultrasound probe, calibration is the process of computing the transformation between the coordinate system of the 2D image and the tracking device attached to the probe. Several different approaches to calibration have been used successfully for 3D systems. The cross-wire phantom method produces accurate calibrations but is extremely time intensive. We present a new calibration method that produces calibrations that are as accurate as those produced by the cross-wire phantom method and are much faster and easier to perform.