Both spinal pain and temporomandibular disorders (TMD) commonly occur in the general population. Previous studies demonstrate neurophysiologic and biomechanical couplings between the trigeminal and cervical regions. This investigation tested the null hypothesis of no relationship between spinal pain (neck, shoulder and/or low back) and TMD, by using questionnaires and clinical examinations of the jaw function. In an age- and sex-matched case-control study, the specific aim was to compare the prevalence of signs and symptoms of TMD among cases with long-term spinal pain and controls without spinal pain. The results showed that subjects with spinal pain had signs and symptoms of TMD significantly more often than did controls. The associations remained after excluding all participants with jaw pain. Furthermore, the comorbidity pattern was similar, regardless of location of spinal pain. In a cross-sectional study, the specific aim was to test whether there is a reciprocal cross-sectional dose-response-like relationship between spinal pain and TMD. Two different designs were used, one with frequency/severity of spinal pain as independent variable, and the other, with frequency/severity of TMD symptoms as independent variable. The analysis showed increasing odds for presence of TMD symptoms with increasing frequency/severity of spinal pain, and increasing odds for presence of spinal pain with increasing frequency/severity of TMD symptoms. In a case-control study within a 2-year prospective cohort, the specific aim was to test whether there is a reciprocal temporal relationship between signs and symptoms in trigeminally, and symptoms in spinally, innervated areas. Incidence of symptoms in these areas was analyzed in relation to presence of spinal pain, headaches, and signs and symptoms of TMD at baseline. The main findings were that presence of signs of TMD at baseline increased the onset of spinal pain and symptoms in the trigeminal area, and that spinal pain increased the onset of symptoms in the trigeminal area. An augmentation effect between the significant baseline variables was observed for the incidence of headaches and jaw pain. In conclusion, the investigation demonstrated a cross-sectional and temporal relationship between spinal pain and TMD; thus, the null hypothesis was rejected. The results indicate common pathophysiological mechanisms in the development of spinal pain and TMD. The comorbidity and reciprocal influence that were found call for an integrated and multidimensional approach in the management of individuals with long-term spinal pain and TMD.