The aim of the study was first to evaluate whether mobility in the cervico-thoracic motion segment is an indicative factor of musculo-skeletal neck-shoulder pain and secondly to compare differences in individual factors between cases and controls for female and male subjects. One-hundred-and-forty-two male electricians and 139 female laundry workers participated in a cross-sectional study. An examination of the Cervico-Thoracic Ratio and a classification of mobility at level C7-T1 was done. All subjects answered a questionnaire about musculo-skeletal complaints. The analysis of relationship between relative flexion mobility in motion segments C7-T5 and neck-shoulder pain showed significant relationships between mobility in specific motion segments and neck-shoulder pain. The overall fit of the multiple regression analysis explained 10% of the variation in neck index (N1) for subjects classified as hypomobile at level C7-T1 and 18% for subjects classified as having an inverse C7-T1 function. Both female and male subjects classified as hypomobile at level C7-T1 showed elevated odds ratios of 2.7 and 2.2, respectively, to have had more than 7 days of neck pain during the previous 12 months, compared to subjects classified as having ordinary mobility at level C7-T1. The factor age showed that young subjects with hypoar hypermobility at level C7-T1 showed elevated odds ratios for neck pain compared to subjects with ordinary mobility in the same age group. In old subjects hypermobility at level C7-T1 was protective compared to subjects with ordinary mobility in the same age group. The factor number of working years showed significant difference between cases and controls among female subjects in the ordinary and hypermobile classes. The factor height showed no significant differences between female or male cases and controls; it did show significant correlation to C7-T1 mobility among female subjects, but not among male subjects. The factors exercise and smoking showed significant differences between cases and controls among female subjects in the ordinary mobility class. The conclusion was that relative flexion mobility is a factor related to the development of neck-shoulder pain rather than the cause of pain.