Measuring cervical spine kinematics in rugby scrummaging is important from an injury prevention perspective. However, choosing an appropriate measurement system is challenging. Since reliability of a measurement system is critical for meaningful interpretation of results, this study evaluated test-retest reliability of an electromagnetic tracking and optoelectronic motion capture system for measurement of cervical spine kinematics during scrummaging. Reliability of joint kinematics at discrete time points was evaluated using intraclass correlation coefficients (ICC), standard error of measurement (SEM), and minimal detectable change (MDC). Reliability of kinematic curves was assessed using coefficient of multiple correlations (CMC) and standard deviations (curve SD). In both systems, seven ICC values were considered to be excellent (> 0.75), while two were fair to good (0.44 - 0.66). Minimal detectable change values for flexion/extension were found to be higher than for other movement directions, and CMC values were only moderate. Overall, reliability was comparable in both systems.