Roentgenographic studies were carried out on 372 patients with tension-type headache and 225 normal control subjects to determine relationships between straightened cervical spines, low-set shoulders, and cervical spine instability. A great majority of the patients with tension-type headache were found also to have straightened cervical spine. Patients with tension-type headache may have a restricted progression of the cervical spinal lordosis, which results in a straightened cervical spine. The flexor muscles of the head and neck prevent physiological lordosis of the cervical spine, and their sustained chronic contraction may be a principal cause of a straightened neck. The low-set shoulder was frequently seen in patients with tension-type headache, and it may result in traction of the brachial plexus, which gives rise to pain in the neck and shoulders. Cervical spine instability, on the other hand, was rather infrequent in patients with tension-type headache. Its relationship to tension-type headache is unclear and warrants further study. Our results suggest that both a straightened cervical spine and low-set shoulders may play an important role in the pathogenesis of tension-type headache and its accessory symptoms.