Sonographic measurements often give considerable diagnostic significance. However, large discrepancy betweenthe real anatomic sizes and sonographic measurements could cause an incorrect diagnosis. Authors carried out aseries of experiment using a phantom and two scanners and the results are as follows: 1. There is a littledifference in errors between two scanners, and the mesurement does not almost always correspond to the realdistance. 2. The rates of errors of the measurements are almost fixed regardless of the positions of thereflcetors. 3. There is no relationship between the transducer MHZ and error rate. 4. As the error is derived from the scanner electronics it is necessary to calibrate the scanner periodically, and if not calibrated one shouldconsider the error rate of the scanner in the anatomical measurement.