To investigate the use of electromagnetic tracking technology for measurement of passive cervical range of motion (ROM). Passive cervical ranges of motion from one extreme to the other were measured in 3 planes (transverse, frontal, and sagittal) by using an electromagnetic tracking system (ETS), the cervical range of motion device (CROM), and visual estimation (VE) with 2 blinded examiners, using a repeated measures design. Swinburne University of Technology, Australia. Four studies were undertaken: (1) Measurement of ROM using 3 methods: the CROM, the ETS, and VE. Two examiners conducted measurements. (2) Measurement of ROM with the CROM and the ETS simultaneously by 1 examiner. (3) Measurement of ROM with the ETS by 2 examiners. (4) Measurement of medium-term reliability of ROM using the ETS over a 24-hour period by 1 examiner. The intraclass correlation coefficient (ICC) was used to investigate the reliability within and between each method and reliability of ROM over a 24-hour period. Study 1: Intra-instrument ICCs ranged from fair to high for the 3 measurement methods. The ETS performed best. Inter-instrument ICCs were poor. Study 2: Direct comparison of the ETS and the CROM yielded high ICCs for rotation and flexion/extension and fair for lateral flexion. Study 3: Interexaminer ICCs using the ETS were high for rotation, good for lateral flexion, and fair for flexion/extension; intraexaminer reliability was high for all planes. Study 4: 24-hour reliability of ROM using the ETS was good for rotation and lateral flexion and poor for flexion/extension. The ETS used in this investigation was an accurate instrument and efficient method for measurement and recording of passive cervical ROM. The ETS had high intraexaminer and fair-to-high interexaminer reliability for the measurement of extremes of ROM in 3 planes. It is probable that differences in the experience levels of examiners did affect interexaminer reliability of the ETS. The ETS and the CROM compared well in rotation and flexion/extension.