Objective: The purpose of this study was to prove the reliability and applicability of a new developed goniometric system to measure the range of motion of the cervical spine by interobserver-repeatability. In addition, it should be examined if there exist age and gender-related differences of the cervical movements. Testing the range of motion of a large quantity of healthy subjects should provide normal values for the cervical movements in three planes. Subjects: 20 patients suffering from neck diseases or complaints were compared with an age- and gender-matched group of healthy subjects. The goniometric method was assessed by five independent examiners (physicians) using interrater-repeatability. Normal values for the cervical mobility were obtained for 220 normal subjects (115 females, 105 males; age: 20 to 78 years). Design: The new developed device consists of a goniometer and a compass, mounted on a 10 x 10 cm(2) plastic sheet. The subjects kept the plastic sheet between the teeth in order to reproduce the three-dimensional mobility of the cervical spine by the range of motion of the occlusion plane. The five independent physicians measured the cervical mobility in all of the 20 patients and 20 asymptomatic volunteers in a randomised and blinded crossover design. The 220 healthy individuals were measured by one examiner. The average values were tested for differences using student's t-test; the interobserver-repeatability was calculated by cross-correlation. Results: The mean values of the range of motion in the three planes were significantly smaller for the patients than for the volunteers (p less than or equal to 0,01 to p less than or equal to 0,001). The interobserver-repeatability both in patients and volunteers was found to be good (0,6 < r less than or equal to 0,08) or even excellent (r > 0,8). This reliability was always significantly higher than arbitrary coincidence (p less than or equal to 0,01 to p less than or equal to 0,001). For the 220 healthy subjects the motion of the cervical spine decreased with age in all three planes. Younger subjects (aged 20-29) showed significantly higher cervical mobility than the elderly (aged 60-69) in all directions (p < 0,001). Women generally showed a greater range of motion than men, the differences being significant for the flexion-extension and for the rotation, but not for the lateral bending. Conclusions: The new developed instrument to measure the cervical spine mobility in three planes is a simple and reliable method with a good interrater-repeatability. The examination procedure was highly accepted in both patients and observers. Because of the pronounced dependence of the cervical mobility on age and gender it is recommended to use age- and sex-related normal values in the diagnosis and follow up of cervical motion restrictions.