Significant errors can occur in ultrasonic systems that measure the distance between separate transmitters and receivers when the transducers are not in angular alignment. This paper describes the results of experiments and numerical simulation to explain and quantify the ranging errors due to angular misalignment between ultrasonic transducer pairs. Two commercially available, 40-kHz piezoelectric transducer pairs are studied (10-and 25-mm diameter). The ranging error is shown to be a predictable function of the orientation angle. © 1990, Acoustical Society of America. All rights reserved.