The authors investigated the effect of neck dimension upon cervical range of motion. Data relating to 100 healthy subjects, aged between 20 and 40 years, were recorded with respect to age, gender and range of motion in three planes. Additionally, two widely used methods of measuring neck motion, chin-sternal distance and uniplanar goniometer, were assessed against a validated measurement tool, the ‘CROM goniometer’. Using multiple linear regression analysis it was determined that sagittal flexion (P = 0.002) and lateral rotation (P\0.0001) were most closely related to neck circumference alone whereas lateral flexion (P\0.0001) was most closely related to a ratio of circumference and length of neck. Hence, assessing cervical range of motion as outcome variable or as a measure at posttreatment follow-up, neck circumference was shown to be one of the factors influencing total neck motion, particularly sagittal flexion and lateral tilt. Comparison of cervical range of motion assessed with a validated measurement tool, the CROM goniometer, with results of both frequently applied clinician’s instruments, the uniplanar goniometer and measurement of chin-sternal distance, showed low reliability with the latter techniques, and motion values measured with these techniques should be interpreted with caution if using them for comparison of cervical range of motion of alike groups. We demonstrated that neck dimension should be incorporated into cervical functional outcome assessment and one should be wary about recorded values for neck motion from non-validated measurement tools.