Background: Evaluation of cervical spine mobility after surgery is mainly based on the measurement of the range of motion during imposed movements. It can thus be questionable if this assessment represents the mobility experienced during daily life. The goal of this study was to propose a new evaluation tool based on the monitoring of cervical spine movement during daily activities. Methods: The detection of cervical movement and the determination of primary motion component (lateral bending, axial rotation or flexion-extension), using two inertial sensors, were first validated in laboratory settings. Fifteen patients who underwent a cervical arthrodesis and nine healthy control subjects were monitored during their daily activity for half a day. The frequency of cervical movement was quantified according to posture, i.e. static and walking periods. The amplitude and velocity of cervical movement were evaluated using the median and cumulative distribution function. Findings: The movement detection and classification showed an excellent performance (sensitivity and specificity > 94%). For the daily monitoring, the patients presented a movement frequency similar to controls, whereas the amplitude and velocity in patients were lower than in controls (P < 0.05). The differences between patients and controls were larger for the velocity parameters (effect sizes > 0.37 and > 0.54 for static and walking periods respectively) than for the amplitude parameters. Interpretation: Body-worn inertial sensors enable the quantitative evaluation of global cervical movement. The movement amplitude and velocity during free-living conditions can be used as objective parameters to evaluate the cervical spine mobility after treatment. (C) 2013 Elsevier Ltd. All rights reserved.